layout/style/test/chrome/test_author_specified_style.html is testing that we get the color value in a way similar to how author specifies it. This basically means we need to have a real implementation of ServoDeclarationBlock::GetAuthoredPropertyValue rather than simply redirecting it to GetPropertyValue. Servo stores an authored string if the value is an identifier, but it doesn't do much otherwise. Also Servo doesn't have a mechanism to distinguish between authored serialization and normalized serialization like Gecko. We may need to add the mechanism to Servo and store some additional information for color there.
There could be some non-trivial work for this in the Servo side (to implement the mechanism distinguishing authored serialization and normalized serialization). This is mostly for devtools support because they need to show the authored one in the panel.
Actually, bug 1349651 is higher priority, so swapping that one out for this one.
I guess this is the same set of code as bug 1349651 though, so probably makes sense for matt to work on this after that one.