Semantic colors

[mathieudutour]

I took a stab at cleaning up the colors used in the project. There is now:

• RAW_COLORS: previously COLORS
• COLORS: the semantic colors
• GRADIENTS: the semantic gradients

There is still a bunch of stuff to do:

• [ ] looking at the shades of blue and purple used. There are many of them and I'm not sure which one would be the primary, secondary, etc.
• [ ] cleaning up the different colors used. Right now I didn't change any color but I didn't create a semantic color for every color we are using (that would defeat the point). So we need to go through the remaining RAW_COLORS and decide whether we want to add a new semantic color, make an exception, or better, change it to use an existing semantic color. cc @joshwcomeau

I updated the colors story to show the semantic colors and the gradients.

[melanieseltzer]

Apologies for the delay here @mathieudutour and thanks for the awesome contribution. We'd love to get this cleaned up and finalized as it's a positive change, would you be interested in continuing work on this?

We were talking on Gitter about primary/secondary/highlight semantic names, and cleaning up the raw colors (like what's listed in your to-list above). We could do this now in this PR, or if you think we should just fix the conflicts so we can merge and just continue with the work afterwards that's fine too, since it seems pretty good to go as is.

Let us know or we'd be happy to take over and deal with getting it finalized if you're no longer interested, no worries at all.

[mathieudutour]

Do take over, it's been a while that I haven't been on this codebase

[superhawk610]

This has been moved to #377.

[melanieseltzer]

Thanks for your work, @mathieudutour :)