Okay, I just googled both "burkini" and "modest swimwear."  There's an awful lot of overlap there.  The burkinis aren't all black, and some of them are very cute. Some of the modest swimwear is also very cute.  I learned about it from a plus-size friend, but I'm sure it's available in all sizes.  I'm too pale to ever go into the water unprotected, so I wear a dive skin.  It's black.  Would the French arrest me too?