The problem is the same in Yakuake and Dolphin.
In the previous versions of Kubuntu, I changed Yakuake colors. To do so I had to close Yakuake, edit my profile in a Konsole window and restart Yakuake.
With Kubuntu 15.04 the modifications are only applied to Konsole and not to Yakuake. I can directly edit my profile in Yakuake, but the modifications are not saved (the colors will be reset next time Yakuake is launched).
Do you know how to permanently apply that kind of modifications?