[css-color-4] Should gray() accept percentage for lightness?

[smfr]

https://www.w3.org/TR/css-color-4/#grays

As the spec says, gray(a / b) is equivalent to lab(a 0 0 / b). However, lab() and lch() both take a percentage as the lightness argument, but gray() is specified to take a number (where 50 is equivalent to 50%). That's confusing if we expect authors to think of gray() as just a shorthand for lab().

So I suggest we spec gray as:
gray() = gray( <percentage> [ / <alpha-value> ]? )

[AmeliaBR]

I strongly agree with this. I don't think we have any other color functions where numbers are mapped in the range 0-100. If we're using a 0-100 range, it makes sense to use a proper percentage type.

[Crissov]

Yes, this the only logical consequences of #4477 (or #3450 and #278), but pending the resultion of #4621. Furthermore, #4494 would perhaps allow gray(50%) to equal gray(0.5), but not gray(50).

[svgeesus]

Agreed, this just needs the edits. I made them for lab() and lch() but failed to also make them for gray().