As I was unhappy with the themes I found, I did begin changing the one that had the most potential for me (thanks for Dark Frost!).
Its not perfect, but very usable for me. Check it out, perhaps somebody else likes it.
And I am open for hints and tips, there are some things I did not find:
- the colour of srcollbars
- the colour of the border of the settings window
- the text colour in the contacts data sheet list (which I hardly use…)