Interestingly, the bright yellow color usually means accident, while orange means regular decompression stop. I have seen pink ones but they seem very rare.
So I'm guessing people must think yellow is more visible?
When I’m doing project diving, we’ll use a pink DSMB to mark something that we want to go back to, and not surface with it.
Orange for surfacing and yellow for an emergency, as you describe.
It a shame that CMAS, PADI or SSI don't propose a standard.
International Orange is designed to be maximally visible under as many different conditions as possible, so may not be the most visible in every single circumstance.