In article , Sacha
writes

How long are you going to leave the paint on for? And are you going t paint
the whole tree/s or just part? I think the answer will be affected by that
information. I would *imagine* that a water based emulsion wouldn't harm
part of a tree if it was washed off immediately.

Modern vinyl emulsions aren't exactly inert though, I suspect - whether
they would actually cause damage, I'm not sure.

Depending on the colour and texture of the bark, could coloured chalks
be used? Or wrap them in coloured papers

I suspect the later comment about painting leaves should not be done -
anything that reduces their access to the sun must be a negative I'd
have thought?

--
regards andyw