If theymos put some restriction/limit on it, like signature space, It can be prevented. If I am not wrong, Only Legendary members' signatures space can use the background color. He can put some restrictions on coloring URLs, too (In my opinion, Coloring URLs should not be allowed for anyone) like Signature space.
What's with people asking for more and more restrictions all the time? Eddie13 sums it up nicely:
Should never have put the temporary illusion of safety above personal liberty..
There are thousands of websites that restrict their users in all possible ways. I don't know any site that offers the same freedom as Bitcointalk. Cherish it, instead of trying to turn it into all the other sites.
Don't forget the forum's mission:
the forum's mission to be as free as possible.
If your safety depends on the color of a link on the internet, maybe the internet isn't for you.