I’ve started seeing more black DSMBs recently. They’re meant to be very visible, but every skipper I’ve spoken to disagrees.

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.

I feel like there is a market for black "tactical" DSMBs for those dudes who really like to be special ops. And what better color than full black to mean serious operator! /s

I've seen plenty of yellow sausages that didn't mean emergency, I think that's location specific (I'm not sure where it applies). Most people I know pick the color based on personal preference / color matching the rest of the gear.

I've only done some diving in the Mediterranean (south of France). And the orange/yellow colors is the "recommended" advice I got from the local dive shops and the common understanding in the diving boats I've been on.

It a shame that CMAS, PADI or SSI don't propose a standard.

When you have high levels of confidence that the background will be ocean water and the weather is likely to be decent (or at least, decent enough to be diving), then it may be the case that yellow is more visible.

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.