The engineering plan mentions supporting a wide range of color values that we'll eventually support. The way we currently handle this is by accepting arbitrary strings and then validating them in the script. However, it would be more efficient and somewhat less prone to bugs if we could catch these errors during schema validation. Based on the engineering document, at least the following values should be supported: - 3-digit and 6-digit hex values - rgb and rgba values - hsl and hsla values
Right now we don't have any special validation for the colors, but if they're not of the 3- or 4-length array type that Chrome uses, then they will get validated as a CSS color when they're applied. If they aren't a valid CSS color, then no value will get applied for that property. There isn't any explicit error presented to the theme author. This doesn't seem like something that we should block enabling on Nightly for. I'll remove this from blocking that bug.