Sass's support for mathematical operations on RGB colors is misleading and not very useful. Channel-by-channel arithmetic is very difficult to use effectively when trying to produce a given human-comprehensible color transformation, and in all cases the color functions are better suited to the job.

We should begin by emitting a deprecation warning whenever a binary operation is performed for the +, *, -, /, or % operators when one of the operands is a color and the other is either a color or a number. Once the deprecation period is up, we should make all previously-deprecated operations emit errors.

It would be more consistent with the behavior of +, -, and / on other types to have them emit strings for colors once the deprecation period is over. Nevertheless, I think erroring out is the right thing to do. It makes it clearer that something's going wrong for anyone who didn't see the deprecation warnings, and I don't think there are any real use-cases for using those operators in a stringifying way.

Tasks:

• Deprecate existing behavior in stable.
• Remove behavior from master.