Experiment using Sass maps to handle project-level configuration.

_color.scss

$brand-color: (
  red:                  #cf383a,
  blue:                 #1f98d4,
  yellow:               #e4cb14,
  white-eggshell:       #f2efe2,
  white:                #000000,
  black:                #ffffff
);

// Returns brand color
@function brand-color($color) {
  @return map-get($brand-color, $color);
}

$site-color: (
  primary:              brand-color(blue),
  secondary:            brand-color(red),
  background:           brand-color(white-eggshell),
  text:                 brand-color(black),
  heading:              brand-color(black),
  text-link:            brand-color(blue),
  text-link-hover:      brand-color(blue)
);

// Returns site color
@function site-color($color) {
  @return map-get($site-color, $color);
}

// Returns either brand or site color, if it exists
// Brand color gets precedence
@function color($color) {
  @return brand-color($color) or site-color($color);
}

_site.scss

a {
  color: color(text-link);
  text-decoration: underline;
  cursor: pointer;

  &:hover {
    color: color(text-link-hover);
    text-decoration: none;
  }
}