Color handling

[uliska]

So far I use coloring as if a color package had been loaded (because in all my test files this is the case).

This has to be handled properly by either

• requiring a color package, or
• disabling color handling when no color package has been loaded.

[uliska]

I think the best option (from a user's perspective) would be:

• Check if color or xcolor is loaded
• If neither is then use xcolor
• In the defaults only use colors available from color
• User can load xcolor with options and then use all colors available through that.