Feature/material design reol 72

Because the coding standard says so. I think the original argument is that lowercase is more readable than upper case.

Since when have any browser changed black or white, which is the primary issue here?

It's not a matter of not knowing what #fff means. Humans instinctively understand natural language better. It's the same reason ASM doesn't use 0xfe21, but calls it "MOV".

If you define $light and $dark, you still have to define $black and $white, as there's times when you need it to be *the* black or white.

Besides, you could just as well argue for #ffffff, rgb(255, 255, 255) or hsl(360, 100%, 100%).