If Im fishing live maggot I buy a pint of mixed and a pint of red, Mixed for throwing in and red for the hook, Any excess reds I have get frozen for bream fishing.
No other colour seems to compare on any fishery I've fished, ever. Thats not to say I won't catch on other colours because I will but reds just give me more action. A good friend of mine swears by white maggots though.
Only time I'll use whites is when I'm fishing for perch, They love a red and white maggot cocktail it seems
I'm no expert so I'm just going by what I've heard - Apparently fish see in shades and red appear as the brightest, probably a load of tosh but red maggots shine everytime I use them!