"David Hill" expounded:

Top fruit planted against walls (Espalier and cordons) was a very important
part of Victorian gardening in the UK, and I have never come across any
reference advocating painting the trunks.
Could be that we don't have the same strength of sunshine here in the UK.

I think it's more the contrast between the strength of the sun and the
extreme cold temperatures many of us deal with. The rapid warm-up of
a dark trunk on a bright sunny day can cause them to split.

--
Ann, Gardening in zone 6a
Just south of Boston, MA
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