How Can One Mix 2 or More Color Palettes to Show a Combined Color Value

How can one mix 2 or more color palettes to show a combined color value

Since I'm more familiar with ggplot, I'll show a solution using ggplot. This has the side benefit that, since the ggplot code is very simple, we can focus the discussion on the topic of colour management, rather than R code.

1. Start by using expand.grid to create a data frame dat containing the grid of red and blue input values.
2. Use the function rgb() to create the colour mix, and assign it to dat$mix
3. Plot.

The code:

dat <- expand.grid(blue=seq(0, 100, by=10), red=seq(0, 100, by=10))
dat <- within(dat, mix <- rgb(green=0, red=red, blue=blue, maxColorValue=100))

library(ggplot2)
ggplot(dat, aes(x=red, y=blue)) + 
  geom_tile(aes(fill=mix), color="white") + 
  scale_fill_identity()

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You will notice that the colour scale is different from what you suggested, but possibly more intuitive.

When mixing light, absence of any colour yields black, and presence of all colours yields white.

This is clearly indicated by the plot, which I find rather intuitive to interpret.

Different colour palettes for two different colour aesthetic mappings in ggplot2

You can get separate color mappings for the lines and the points by using a filled point marker for the points and mapping that to the fill aesthetic, while keeping the lines mapped to the colour aesthetic. Filled point markers are those numbered 21 through 25 (see ?pch). Here's an example, adapting @RichardErickson's code:

ggplot(currDT, aes(x = EFP, y = SAPT), na.rm = TRUE) +
  stat_smooth(method = "lm", formula = y ~ x + 0, 
              aes(linetype = Halide, colour = Halide), 
              alpha = 0.8, size = 0.5, level = 0) +
  scale_linetype_manual(name = "", values = c("dotdash", "F1"),
                        breaks = c("hal", "non-hal"), labels = c("Halides", "Non-Halides")) +
  geom_point(aes(fill = Anion, shape = Cation),  size = 3, alpha = 0.4, colour="transparent") +
  scale_colour_manual(values = c("blue", "red")) +
  scale_fill_manual(values = my_col_scheme) +
  scale_shape_manual(values=c(21,24)) +
  guides(fill = guide_legend(override.aes = list(colour=my_col_scheme[1:8],
                                                 shape=15, size=3)),
         shape = guide_legend(override.aes = list(shape=c(21,24), fill="black", size=3)),
         colour = guide_legend(override.aes = list(linetype=c("dotdash", "F1"))),
         linetype = FALSE)

Here's an explanation of what I've done:

1. In geom_point, change colour aesthestic to fill. Also, put colour="transparent" outside of aes. That will get rid of the border around the points. If you want a border, set it to whatever border color you prefer.
2. In scale_colour_manual, I've set the colors to blue and red, but you can, of course, set them to whatever you prefer.
3. Add scale_fill_manual to set the colors of the points using the fill aesthetic.
4. Add scale_shape_manual and set the values to 21 and 24 (filled circles and triangles, respectively).
5. All the stuff inside guides() is to modify the legend. I'm not sure why, but without these overrides, the legends for fill and shape are blank. Note that I've set fill="black" for the shape legend, but it's showing up as gray. I don't know why, but without fill="somecolor" the shape legend is blank. Finally, I overrode the colour legend in order to include the linetype in the colour legend, which allowed me to get rid of the redundant linetype legend. I'm not totally happy with the legend, but it was the best I could come up with without resorting to special-purpose grobs.

NOTE: I changed color=NA to color="transparent", as color=NA (in version 2 of ggplot2) causes the points to disappear completely, even if you use a point with separate border and fill colors. Thanks to @aosmith for pointing this out.

Can I mix two UIColor together?

You can't mix two UIColors directly as you mention in your question. Anyways there is an example to mix two colors using other schemes. The link for same is as follows:

Link Here

Leaflet: Mixing continuous and discrete colors

Since the sample above is not enough to have a demonstration, I decided to use one of the dummy data that I used for other leaflet related questions. I hope you do not mind that. Given what you said, you need to create two layers in your map. One for a continuous variable, and the other for a discrete variable. This means that you need to create two sets of colors. As you used, you want to use colorNumeric() for the continuous variable. You want to use colorFactor() for the discrete variable. In my sample code, I create a new discrete variable called group. Once you finish creating the color palettes, you want to draw a map. You need to use addPolygons() twice. Make sure that you use group. This is going to appear in the layer control button on the right upper corner. As far as I know, we cannot display one legend only at the moment. I came across this issue before and concluded that we have no choice at the moment. I hope this demonstration is enough for you to make a progress in your task.

library(raster)
library(dplyr)
library(leaflet)

# Get UK polygon data
UK <- getData("GADM", country = "GB", level = 2)

### Create dummy data
set.seed(111)
mydf <- data.frame(place = unique(UK$NAME_2),
                   value = sample.int(n = 1000, size = n_distinct(UK$NAME_2), replace = TRUE))

### Create a new dummy column for a discrete variable.
mydf <- mutate(mydf, group = cut(value, breaks = c(0, 200, 400, 600, 800, 1000),
                                 labels = c("a", "b", "c", "d", "e"),
                                 include.lowest = TRUE))

### Create colors for the continuous variable (i.e., value) and the discrete variable.
conpal <- colorNumeric(palette = "Blues", domain = mydf$value, na.color = "black")
dispal <- colorFactor("Spectral", domain = mydf$group, na.color = "black")

leaflet() %>% 
addProviderTiles("OpenStreetMap.Mapnik") %>%
setView(lat = 55, lng = -3, zoom = 6) %>%
addPolygons(data = UK, group = "continuous",
            stroke = FALSE, smoothFactor = 0.2, fillOpacity = 0.3,
            fillColor = ~conpal(mydf$value),
            popup = paste("Region: ", UK$NAME_2, "<br>",
                          "Value: ", mydf$value, "<br>")) %>%
addPolygons(data = UK, group = "discrete",
            stroke = FALSE, smoothFactor = 0.2, fillOpacity = 0.3,
            fillColor = ~dispal(mydf$group),
            popup = paste("Region: ", UK$NAME_2, "<br>",
                          "Value: ", mydf$group, "<br>")) %>%
addLayersControl(overlayGroups = c("continuous", "discrete")) %>%
addLegend(position = "bottomright", pal = conpal, values = mydf$value,
          title = "UK value",
          opacity = 0.3) %>%
addLegend(position = "bottomleft", pal = dispal, values = mydf$group,
          title = "UK group",
          opacity = 0.3)

If you choose the continuous-variable layer, you will see the following map.

If you choose the discrete-variable layer, you will see the following map.

Update

If you want to show both a continuous group and a continuous group together, you need to subset your data beforehand so that there is no overlapping in polygons. Using UK and mydf above, you can try something like this.

### Subset data and create two groups. This is something you gotta do
### in your own way given I have no idea of your own data.

con.group <- mydf[1:96, ]
dis.group <- mydf[97:192, ]

### Create colors for the continuous variable (i.e., value) and the discrete variable.
conpal <- colorNumeric(palette = "Blues", domain = c(min(mydf$value), max(mydf$value)), na.color = "black")
dispal <- colorFactor(palette = "Reds", "Spectral", levels = unique(mydf$group), na.color = "black")

### Subset the polygon data as well

con.poly <- subset(UK, NAME_2 %in% con.group$place)
dis.poly <- subset(UK, NAME_2 %in% dis.group$place)

leaflet() %>% 
addProviderTiles("OpenStreetMap.Mapnik") %>%
setView(lat = 55, lng = -3, zoom = 6) %>%
addPolygons(data = con.poly, group = "continuous",
            stroke = FALSE, smoothFactor = 0.2, fillOpacity = 0.3,
            fillColor = ~conpal(con.group$value),
            popup = paste("Region: ", UK$NAME_2, "<br>",
                          "Value: ", con.group$value, "<br>")) %>%
addPolygons(data = dis.poly, group = "discrete",
            stroke = FALSE, smoothFactor = 0.2, fillOpacity = 0.3,
            fillColor = ~dispal(dis.group$group),
            popup = paste("Region: ", UK$NAME_2, "<br>",
                          "Group: ", dis.group$group, "<br>")) %>%
addLayersControl(overlayGroups = c("continuous", "discrete")) %>%
addLegend(position = "bottomright", pal = conpal, values = con.group$value,
          title = "UK value",
          opacity = 0.3) %>%
addLegend(position = "bottomleft", pal = dispal, values = dis.group$group,
          title = "UK group",
          opacity = 0.3) 

Mixing two colors naturally in javascript

I dedicated 3-4 days to this question. It's a really complex problem.

Here is what you can do if you want to mix two colors "naturally":

1. CMYK mixing: it's not the perfect solution, but if you need a solution now, and you don't want to spend months with learning about the subject, experimenting and coding, you can check this out: https://github.com/AndreasSoiron/Color_mixer

2. Implementing the Kubelka-Munk theory. I spent a lot of time reading about it, and trying to understand it. This should be the way to go if you want a professional solution, but it needs 6 parameters (like reflectance, absorption, etc.) for each colors you want to mix. Having R, G, B isn't enough. Implementing the theory isn't hard, but getting those parameters you need about each color seems to be the missing part. If you figure it out how to do it, let me know :)

3. Experimental: you can do something what the developers of the ipad app: Paper have done. They manually selected 100 pairs of popular colors and eyeball-tested how they should blend. Learn more about it here.

I personally will implement the CMYK mixing for the moment, and maybe later, if I have time I'll try to make something like the guys at Fiftythree. Will see :)

Combine legends for color and shape into a single legend

You need to use identical name and labels values for both shape and colour scale.

pd <- position_dodge(.65)
ggplot(data = data,aes(x= year, y = beta, colour = group2, shape = group2)) +    
  geom_point(position = pd, size = 4) +
  geom_errorbar(aes(ymin = lcl, ymax = ucl), colour = "black", width = 0.5, position = pd) +
  scale_colour_manual(name = "Treatment & State",
                      labels = c("Control, Non-F", "Control, Flwr", "Exclosure, Non-F", "Exclosure, Flwr"),
                      values = c("blue", "red", "blue", "red")) +   
  scale_shape_manual(name = "Treatment & State",
                     labels = c("Control, Non-F", "Control, Flwr", "Exclosure, Non-F", "Exclosure, Flwr"),
                     values = c(19, 19, 17, 17))

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