chemical reactions

Asserting up front that this was an awful waste of fresh tomatoes, we just tried making bloody mary mix from scratch and had something very strange happen. We're hoping someone with some chemistry knowledge can help explain it. Following a standard recipe, we put into a blender the following...

And not just the fact that no-one outside the Netherlands can pronounce his name! It would appear that the chrome based yellows in his paintings are turning brown, probably due to exposure to light. A shame, means that they will have to be kept in the dark and only brought out for occasional...