What's Default HTML/CSS Link Color

a {
  color: inherit;
}

<p>The default color of the html element is black. The default colour of the body and of a paragraph is inherited. This
  <a href="http://example.com">link</a> would normally take on the default link or visited color, but has been styled to inherit the color from the paragraph.</p>

HTML default link color

Even if you don't change the default color, it would still be a good idea to specify the color to ensure that it looks the same in all browsers. I'd put something like this in the stylesheet:

a, span.link {
  color: blue;
}

a:visited, span.visited {
   color: purple;
}

a:active, span.active {
   color: red;
}

Then you can style spans as links by <span class="link">Your fake link</span>

Default color from link won't change

You need to apply this style to the <a> tag, not the <span>. But more importantly, you're using the same id of links twice, which is not legal. Change it to a class instead:

<p>Viens voir toute la team NoMaD en action! Disponible sur <span id="links"><a href="https://www.youtube.com/channel/UCx9wXRznZvavCSXkbrJoDYw?view_as=subscriber">YouTube</a></span>, <span class="links"><a href="https://www.twitch.tv/teamn0mad">Twitch</a></span>, et  <span class="links"><a href="https://www.instagram.com/la_team_nomad">Insta</a></span>.</p>

Then change your CSS to select on this class instead of the id:

.links a {
    color:inherit;
    text-decoration:none;
    transition:color 1s;
}

.links a:hover {
    color:white;
}

How can I change link color in html email?

Thanks to mplungjan I realised that my solutions were wrong and it's an easy fix.
Thank you for everyone who posted solutions!

<a href="www.xyz.com" style="text-decoration: none; color: #959595; cursor: pointer">www.xyz.com</a>

CSS a:link keep original color

Try this in your stylesheet:

a:link {
   color:inherit;
}

Note that you then probably should make sure you have some other way to identify links, or your users will be confused. (I.e. don't remove the underlining, too.)

If you want to deal with browsers not supporting inherit, I suppose repeating the definition which originally set your color will do.

As an example, assume the class important should be shown in red:

.important {
    color:red;
}

.important a:link {
    color:red;
}

But of course it is not nice to have to double all color indications. I assume one could do something in JavaScript (looping through all the a elements and giving them the right class explicitly). (I have no IE available to test this.)

Is there a way to unset an 'a' tag link to the default color

The value for original setting you're looking for is called initial.

a:hover {
    color: initial
}

However, that might make the link black. Which means it wouldn't work for you in this case. You can get around this another way though, through your a style. Use the inverse of :hover using the :not selector.

a:not(:hover){
  color: #000;
  text-decoration: none;
}

<a href="#">Hi, I'm Link.</a>

a:link    { color: black; }
a:visited { color: black; }

a:not(.default):link    { color: black; }
a:not(.default):visited { color: black; }