Not really, you only need two, and only one of those (the red one) needs to be substantial enough to be used as an ascent platform, and have a reel attached. The other (yellow) one can be much thinner and doesn't need a reel.
I quite often see DSMBs with red on one side and yellow on the other. I really can't see the point of those, although admittedly they can be easy to spot in rough water. I was surprised to see that AP Valves make them in the UK - I thought they would have known better.
A couple more comments. I don't see the point of the "safety sausages" so beloved of (primarily) American recreational divers, and also used by many DMs here in Belize. They're only any use on the surface to wave to try to attract the boat's attention, and only have a couple of metres' line, if any. The real benefits of deploying a DSMB from a reel are (1) to show the boat where you are as you start your ascent, especially if there's much of a current, and (2) to provide you with an ascent platform (you make yourself slightly negative and hang from it). Not deploying until you're on the surface is rather missing most of the point.
And I wish more people would use DSMBs on every dive as a matter of routine, rather than as here regarding them as an admission of failure. I've had people say to me that they don't need them because their boat captains are able to track bubbles, and they don't need an ascent platform because they have really good buoyancy control. Again, rather missing the point.
