Few days ago, I installed a phpbb forum system for the UO shard I used to play on. This forums allow a lot of features and customization, from posting in different colors to changing the forum theme/style on a per-user basis.
I installed a dark, WoW-style theme, and the staff created a variant with brighter, brown colors.
The problem came when the users started writing posts in colors. Ones writing in dark green, others in pink, bright red... All who used bright colors were readable with the dark theme, but not on the brown/light one, and viceversa.
We tried telling the users to respect their companions and writing in standard/default color only (as the default color changes with the theme to be readable always), and the effect was the opposite: even more people writing in colors and trying to force the rest of the users to use their chosen theme.
So... we had to cut off their freedom, and after a bit of research I found and installed the User Disable Colored Text MOD. Now everyone writes in the default color, and while it's a bit monotonous, at least we enforce respect for the rest of the users.
It's a pity to have sometimes to force respect, when you've got the option to do whatever you want.