I see a lot of repetitive code and faulty assumptions regarding colors, which are handled often within ES/JS, because of its close association with CSS. For many coders, a color apparently is always a 24-bit sRGB value expressed as a 6-digit hexadecimal number (or 3-tuple) preceded by a hash sign, e.g. #ABCDEF or #f00ba7.
I believe this could be improved a lot if there was a Color "datatype" built into ES-262, similar to Number or Date, or at least a global object Color that provided common functions like Math does.
In its current state at least, CSS OM does not seem to address anything near what I had in mind. It's just about parsing and serialization, not about manipulation, conversion etc.
See the https://www.w3.org/TR/css-typed-om-1/, which is primarily about things like CSS.px(1) and other value types. I mistakenly thought this was part of CSSOM, but it's a separate proposal on top of it.