Your room sounds lovely, and I have a few ideas for adding to the loveliness:
Since your beams are foam, painting them a solid color is a missed opportunity to add character to your space. If I were you, I'd go with a faux finish technique - a base coat with a topcoat grained over it to make it look like a pickled wood or a limed wood. Or you could finish it in darker tones to give the impression of grain and an aging effect. An approach along these lines will make it more of a neutral to add antique-y texture. I almost always suggest mixing different periods of things, like a worn finish amidst contemporary pieces, to make a room more interesting.Another option is a crackle coat to give an aging effect - all paint manufacturers make a crackle base. Whichever route you take, think about putting a deeper, warmer tone on first, followed by a lighter, more antique-y tone on top. It'll add texture and richness. But whatever you do, avoid a solid color - that would be a missed opportunity for your high ceiling space! Foam can look shockingly realistic if you treat it the right way.