I posted this picture (reversed!) ages ago; it's The Fair Isle Jumper by Stanley Cursiter, and today I saw the real thing - the jumper itself, that is:
According to the catalogue of the National Museum of Scotland here in Edinburgh where the garment is on display in the Fashion & Style gallery, it dates from 1910, but Cursiter painted his picture in 1923. Did he borrow it from the collection for the purpose? I'd like to know more about the painting's backstory (and I love the blue scarf).
On the subject of Fair Isle knitting, I recommend the Fruity Knitting podcast presented by Andrew and Andrea. While Andrew is fairly new to the needles, his wife Andrea is a highly accomplished knitter, and her Alice Starmore colourwork in particular is awe-inspiring.