I don't care what color we wear, yellow shirts over green pants
would work, as long as we
stop wasting money on changes just to be pretty and every sanction having to be different. 
You fashion dilettantes should give up, it's a job not a fashion show.
As far as heat, fabric means more than color and yes the old, old shirts could be uncomfortable for wimps. Although I agree the new fabric is more practical, less sweat damage, no ironing, etc.
There is no ball game anywhere that can not be umpired in
the same uniform as any other game, regardless of what color that is, including powder blue over navy.