How to Change Placeholder Color on Focus

input:focus::placeholder{
    color: blue;
}

<input placeholder="ding">

Changing color of placeholder text on focus with JavaScript

Believe you need vendor prefixes (From css-tricks.com):

::-webkit-input-placeholder {
   color: red;
}

:-moz-placeholder { /* Firefox 18- */
   color: red;  
}

::-moz-placeholder {  /* Firefox 19+ */
   color: red;  
}

:-ms-input-placeholder {  
   color: red;  
}

Using javascript you would only be applying similar styling (using vendor prefixes) programmatically on a focus event.

Edit: In fact these styles I don't think can be applied using javascript. You would need to create a class and apply that using js.

CSS:

input.placeholderred::-webkit-input-placeholder {
   color: red;
}

JQuery:

var $textInput = $('#TextField1');
$textInput.on('focusin',
    function () {
         $(this).addClass('placeholderred');
    }
);

$textInput.on('focusout',
    function () {
         $(this).removeClass('placeholderred');
    }
);

JS:

var textInput = document.getElementById('TextField1');
textInput.addEventListener('focus',
    function () {
         this.classList.add('placeholderred');
    }
);

textInput.addEventListener('blur',
    function () {
         this.classList.remove('placeholderred');
    }
);

And courtesy of the most helpful, Armfoot, a fiddle: http://jsfiddle.net/qbkkabra/2/

Change a HTML5 input's placeholder color with CSS

Implementation

There are three different implementations: pseudo-elements, pseudo-classes, and nothing.

• WebKit, Blink (Safari, Google Chrome, Opera 15+) and Microsoft Edge are using a pseudo-element: ::-webkit-input-placeholder. ^[Ref]
• Mozilla Firefox 4 to 18 is using a pseudo-class: :-moz-placeholder (one colon). ^[Ref]
• Mozilla Firefox 19+ is using a pseudo-element: ::-moz-placeholder, but the old selector will still work for a while. ^[Ref]
• Internet Explorer 10 and 11 are using a pseudo-class: :-ms-input-placeholder. ^[Ref]
• April 2017: Most modern browsers support the simple pseudo-element ::placeholder ^[Ref]

Internet Explorer 9 and lower does not support the placeholder attribute at all, while Opera 12 and lower do not support any CSS selector for placeholders.

The discussion about the best implementation is still going on. Note the pseudo-elements act like real elements in the Shadow DOM. A padding on an input will not get the same background color as the pseudo-element.

CSS selectors

User agents are required to ignore a rule with an unknown selector. See Selectors Level 3:

a group of selectors containing an invalid selector is invalid.

So we need separate rules for each browser. Otherwise the whole group would be ignored by all browsers.

::-webkit-input-placeholder { /* WebKit, Blink, Edge */
    color:    #909;
}
:-moz-placeholder { /* Mozilla Firefox 4 to 18 */
   color:    #909;
   opacity:  1;
}
::-moz-placeholder { /* Mozilla Firefox 19+ */
   color:    #909;
   opacity:  1;
}
:-ms-input-placeholder { /* Internet Explorer 10-11 */
   color:    #909;
}
::-ms-input-placeholder { /* Microsoft Edge */
   color:    #909;
}

::placeholder { /* Most modern browsers support this now. */
   color:    #909;
}

<input placeholder="Stack Snippets are awesome!">

:focus::-webkit-input-placeholder {
   color: blue;
}
:-moz-placeholder:focus {
   color: blue;
}
:-ms-input-placeholder:focus {
   color: blue;
}

  .mat-focused .mat-form-field-label {
      /*change color of label*/
      color: red !important;
  }

 .mat-form-field-underline {
   /*change color of underline*/
    background-color: blue !important;
 } 

.mat-form-field-ripple {
   /*change color of underline when focused*/
   background-color: yellow !important;;
 }