Make method generating colors for new users more efficient
Make method generating colors for new users more efficient

There is no need to retrieve the actual user objects, only their amount
is needed.

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