This has already happened in HK, as Hong Kongers use masks to protect their identity and to express themselves during the protests

Quite a few already doing that.

I know over at coquetryclothing.com they used to decline to make masks due to possible liability reasons. Now they are making custom ones with all manner of fabrics.

Maybe after things have settled down. Right now, the right thing to do is to hand those out free to everyone, to normalize the safe behaviour. You can make your buck later.

Funky bicycle masks with colors or logos were often 30-80€ in 2016, and despite not being even FFP1. There is an opportunity, but there is also a feeling that health apparel should be bland and ugly if they are serious. It’s like wearing a suit at a programmer interview: Often a hint that one aspires more to the commercial side than the technical side, despite both being competent.

that's an interesting idea! I've seen personalized welding masks. You'd have to make sure it doesn't interfere with the functioning of the mask. Just producing them in different colors would be a start.