Improve color name pattern

[AndyScherzinger]

While reviewing #4762 I realiszed that the naming pattern of the colors isn't consistent mixing lowercase+underscore and camelCase pattern. In general resource names in our code base are lowercase+underscore.
Looking at color names, things that need to be corrected have to be checked in colors.xml (day/night) as well as setup.xml, e.g.

first step for #4278