Either you or I misread the question. I think it wasn't about selling a copy. It was about using copying to learn how to paint (which is fine, as you've stated) and then produce your own painting which you then sell. The sold painting isn't a copy. So .. no copyright infringement?
Ah, I think it depends how you interpreted the question. I took 'new painting' to mean a copy of other painter's work.
Looking at it from your perspective(which on reflection is the right interpretation), I would say no copyright infringement assuming the 'new painting' is an original creation i.e. not a duplicate of an existing piece of art by another artist.
Plenty of people, myself included, learn creative arts by mimicking others and then developing our own style which might be similar to the artists we got our inspiration from. I think as long as it's clear that there is no duplication of the original works(for sale), then all is okay.
So if I learnt my art by mimicking Van Gogh and my new paintings are of a similar Van Gogh style, as long as they are original creations, no copyright infringement imo.
