The National Gallery has had an exhibition (now closed, sadly) of two of Van Gogh's famous sunflower paintings. Here is a photo of them from the BBC website:
I was reading up on these and learnt that one of the reasons they were so revolutionary, is that Van Gogh "broke all the rules" and placed the flowers on a background of the same colours as the subject (the received wisdom - now as then - is that the background "should" contrast or complement). And I realised where I had been going wrong with my attempts at complementary backgrounds. So I painted the collie on a muted version of the colours in his own coat. I like it.