[@akira010203 Participant 10 years, 5 months ago]

I found out where is the problem.

It is due to the language translation file, If I put the default language back in english there is no problems.

To the french users if you get this issue try :

#bbpress-forums .administrateur .bbp-author-role {
  background-color: blue;

It will wrk but when it comes to the french translation of moderator : modérateur it will be harder due to the special character on it.

You will have to rename it before being able to change color.