I got this back from A. Krauss at Avantgarde when I asked the same question.
"Q3) It is not very complicated to detach the horns, but we do not recommend to repaint them (exception: plain white horns, which are made from non-lacquered polished white plastic). For further advise you may let us know which colour you have and to which colour you want to change.
"
"Q3) It is not very complicated to detach the horns, but we do not recommend to repaint them (exception: plain white horns, which are made from non-lacquered polished white plastic). For further advise you may let us know which colour you have and to which colour you want to change.
"