I have older primary boys. I get that their choice of high street clothes is a dull range of maroon, grey, navy and khaki for summer. It is indeed depressing.
But whether we like it or not, gendered clothing does currently exist & those are 100% girls shorts.
As PP said - if he feels strongly that he likes the gingham that's one thing, but putting him in them just because you don't like grey shorts is completely another. This is a kids preference first situation.
Aside from that, the gingham bloomers are not a good-looking alternative anyway.