Not knocking, just my experience

. To each their own, I just am more surprised that, foam core is the statuesque. Foam core fades in any light other than complete blackness. As far as painting foam core I guess you could, but why would you paint paper, It would most likely just sink in or cover really weird. I just hate foam core, yes I said it, I am a foam core hater. It smashes under any pressure, edges tear when you cut it wrong, and does not like any moisture/humidity. I have cut and used about 200 football fields of the stuff, and with all the things you could do with it, I would not say a permanent/semi-permanent bezel is the best. Hell it will get the job done though.
To follow up though, that plastic light diffuser sheeting is awesome, cheap, and paints very well. Just offering up a alternative that I found very useful.