It's B-2 not B-12!

RDA of B-2 is 1.7 mg so take enough that gets you 10 mg or higher. Most B supplements have 25 mg, most daily vitamins have 1.7 mg. Taking a lot won't hurt you but it can upset your stomach.

Color isn't that important unless it is an instant test.

If the drink has a lot of fiber in it, go for it. Remember its volume during dilution.