Make RGBAField create RGBA objects also from unicode
Make RGBAField create RGBA objects also from unicode

This caused the test fixture not to be loaded correctly. The color of
the textlabels was not read in correctly and caused the created RGBA
object to have its default values.

htem/CATMAID,htem/CATMAID,fzadow/CATMAID,htem/CATMAID,fzadow/CATMAID,fzadow/CATMAID,fzadow/CATMAID,htem/CATMAID