Eliminate special case code for certain CSS attributes

This is a follow-on to JDK-8274699.

The FX CSS parser has special case logic to parse certain attributes where some values match color values. For example, see the following:

https://git.openjdk.java.net/jfx/blob/c6f4ff01f2af7d2616b0b49a51ded3ec69f7b0a5/modules/javafx.graphics/src/main/java/javafx/css/CssParser.java#L817

This is error prone, so we should look for more general approach.