Please add subtract_color(minuend, subtrahend) to allow porting code relying on color subtraction to sass-4 more easily

When I try to compile this on sass-4 (dart-sass), I get an error:

.a {
  x: white - grey;
}

Error: Undefined operation "white - grey".
  x: white - grey;
     ^^^^^^^^^^^^
  - 2:6  root stylesheet

I found that to port my code, I had to write this, which is quite WET (see how many times I have to write grey) and tedious:

.a {
  x: adjust_color(white, $red: -(red(grey)), $green: -(green(grey)), $blue: -(blue(grey)));
}

May a subtract_color(minuend, subtrahend) be added which implements the sass-3 color minus color support to enable easier porting of sass-3 code to sass-4? I can always write one myself for my own code, but I think it should be core.

Thanks.

[nex3]

We’re removing color arithmetic because it doesn’t mean anything in terms of actual colors as humans perceive them, and we want to encourage users to use the color functions that do have comprehensible semantics. Adding new functions to do the same thing would defeat that purpose. As far as migration goes, it’s pretty easy to write your own functions that do the same thing as arithmetic, as you’ve demonstrated.

[binki]

I think I would expect such functions to match the behavior provided by the following:

@function add_color($a, $b) {
  @return adjust_color($a, $red: red($b), $green: green($b), $blue: blue($b));
}
@function subtract_color($minuend, $subtrahend) {
  @return adjust_color($minuend, $red: -(red($subtrahend)), $green: -(green($subtrahend)), $blue: -(blue($subtrahend)));
}

@function multiply_color($a, $scalar) {
  @return rgba($scalar * red($a), $scalar * green($a), $scalar * blue($a), alpha($a));
}
@function divide_color($a, $scalar) {
  @return rgba(red($a) / $scalar, green($a) / $scalar, blue($a) / $scalar, alpha($a));
}

.a {
  x: subtract_color(white, grey);
  y: add_color(green, red);
  z: multiply_color(grey, 2);
  w: divide_color(green, 2);
}
.b {
  x: subtract_color(rgba(255, 254, 253, .4), grey);
  y: add_color(rgba(0, 254, 253, .4), red);
  z: multiply_color(rgba(255, 254, 253, .4), 2);
  w: divide_color(rgba(255, 254, 253, .4), 2);
}

output:

.a {
  x: #7f7f7f;
  y: #ff8000;
  z: white;
  w: #004000;
}

.b {
  x: rgba(127, 126, 125, 0.4);
  y: rgba(255, 254, 253, 0.4);
  z: rgba(255, 255, 255, 0.4);
  w: rgba(128, 127, 127, 0.4);
}