My reaction to the OP (assuming it to be a genuine question) would be the same whether it were
Gingham shorts
A princess dress
A superhero costume
A dinner jacket and trousers
A hand-knitted jumper depicting Postman Pat
or anything else you may wish to name, that isn't on the uniform list.
My view is that school is a community, and uniform gives children a shared identity and makes dressing them easier and cheaper, and removes competition and focus on clothes at school. Basically, the usual reasons why people are pro uniform, which you clearly don't share. (So let's not have a debate about uniform itself).
I also, more strongly, believe parents should work with the school in good faith, and model a constrictive and positive relationship, not dive headfirst into quibbling over petty things like grey shorts. It's a confusing and unhelpful message to send your kid - "You're starting school! It's going to be great! But they want all the boys to wear these grey shorts, and I think these gingham ones are nicer, so I'll see if you can wear those".
I find that young children are generally fine with uniform. I have one child who is very particularly about what they wear and really enjoys choosing clothes. Yet they never had a moment's hesitation about school uniform in the Infants. I mean, standard morning routine whingeing, sometimes yes. Deep-rooted philosophical issues about the clothes, no. I know other parents who were worried whether their Reception starter would accept the uniform, and lo and behold, they all did. They saw that the other girls/boys wear it, and so they also happily wore it.
My kids' school doesn't have variations for the uniform, beyond summer/winter and girls/boys. The school community is generally happy with that. There is no reason for the kids not to be in uniform as there's a plentiful supply of extremely cheap second hand uniform, and I don't notice kids deviating from the uniform.
I know of other schools in the area which have a much more "mix and match" uniform policy, which to me looks like a tremendous ball ache, a recipe for kids being picky and chopping and changing for the sake of it (I know mine probably would, and I don't have time for it in the mornings).
I think it's a bit strong to casually call people bigots, and what you say basically sounds like Bart Simpson slapping Lisa in the back of the car and saying "stop slapping yourself, why are you slapping yourself". And why am I - maybe I will go to bed instead.