Question

why does some fuels have red flame
Like hydrogen ​

Answer 1

Because some fules react with oxygen to change its Colour.

Answer 2

oxygen (or air) and an ignition source

are required for combustion to occur hydrogen burns with a pale blue flame tha is nearly invisible in daylight. the flame may appear yellow if there are impurities in the air like dust or sodium.

A pure hydrogen flame will not produce smoke.

this help you