Hum, I have found a related message in the forum, entitled "debian sid - yellow selection, not saved priority" (for the title I could not imagine). The proposed solution there is:
But I have changed "Color scheme" in Control Center -> Appearance & Themes -> Colors -> Color Scheme and everything is ok now.
The problem is that in my Ubuntu you have not the posibility of changing colors (they think you better do not change anything because you can make it bad

).
Anyway, I think that this is an amule bug, because the program should ensure that the text color is readable within the background color, isn't it?
Any hint for ubuntu users? ?(