Brand Colors is the most comprehensive source of hex color keys I’ve come across. Easily choose from ASE, SASS, LESS, or CSS formats and download the hundreds of colors available or roll your own collection with only those you need. Alternatively, quickly search and grab that one color right away with no further need for a Google search.

I download the whole set and build my own using Sass:

// long list of brand colors here:
// ...
$bc-facebook: #3b5998;
// ...
$bc-github: #4183c4;
$bc-github-2: #999999;
$bc-github-3: #666666;
$bc-github-4: #333333;
$bc-github-5: #6cc644;
$bc-github-6: #bd2c00;
$bc-github-7: #ff9933;
// ...
$bc-twitter: #55acee;
// ...
$bc-youtube: #cd201f;
// ... + many more
// make a list of the brand colors you wish to use
$logo-color-list: (
github $bc-github-4,
twitter $bc-twitter,
youtube $bc-youtube
);
// make whatever classes you need from the list above
@each $social-media-service, $logo-color in $logo-color-list {
.#{$social-media-service}:hover {
color: $logo-color;
}
}

Sass will loop over the items in $logo-color-list to produce CSS derived from the @each statement:

.github:hover {
color: $333333;
}
.twitter:hover {
color: $55acee;
}
.youtube:hover {
color: $cd201f;
}

Notice that only the items added to $logo-color-list show up in the final CSS. There’s no need to worry about the variables from the master brand color list. If they aren’t used, they won’t show up in your CSS. Nice!