Ok, some hints,
I notice that it comes from my customized desktop color sheme (appearance). When I revert to a standard color sheme, the language indicator turns dark blue again after reboot.
So, internat.exe picks its color from the desktop color sheme applied. Therefore I re-edited my personalised color sheme changing every item where this color appeared. I found it on one place: On "active title text". I changed this color to dark blue. rebooted, and... the light blue color was back!
Eventhought there is NO white blue color in the new sheme!
I realy wonder where it finds this color.