Hi Norbert,

That is very interesting! Yes, it looked almost exactly like the
photo's behind the link. So the colouring is caused by a trapped
nerve, which could be caused by a cyst or tumor, which could originate
from internal bacterial infections (acccording the website). Certainly
a few points to check and look out for next time. Interesting that the
colouring almost disappeared again, maybe it recovered, and then had a
fatal setback. Interesting photo's, I need to photograph my fishes
more. Thanks!

Hendrik