Add support for CIELAB (LCH/HCL)

[superhighfives]

Is your feature request related to a problem? Please describe. CIELAB (LCH/HCL) is coming to CSS with the L4 Color Spec (https://www.w3.org/TR/css-color-4/#resolving-lab-lch-values) so they'll be more mainstream in the not too distant future.

Describe the solution you'd like Support viewing colours in CIELAB.