What should I tell him (read details)?

What's wrong with complimenting paintings? He'll probably be really happy someone said something nice about them. But if you decide to strike up a conversation, make it something that he has to respond to with something more than a thanks! Ask him a question about the painting or its inspiration. My boyfriend used to be really shy around me. I just asked questions about common interests and worded them so he had to give more than a one-word response. Good Luck!