Death of a Ghost by Margery Allingham
I do have a fondness for mysteries involving art. In Death of a Ghost, a young artist is killed at the showing of a painting, not his painting, one of his mentor's, Lafcadio. Lafcadio, before he died, left instructions to have one of his paintings that he had boxed up shown each year beginning several years after his death, and his wishes have been faithfully carried out by his widow- quite a strong woman by the way, the kind of woman who takes everything life throws at her, straightens her shoulders, and carries on. Campion, luckily, was at the party/showing, so even though he didn't actually witness the murder, as a friend of the family he takes an interest in the mystery.
There is a lot of art talk in this one, which I find fascinating. I even took a picture of at least one page and sent it to Amber, since the description of the area where the paint was...