Do you milliput or some other brand? What brand of putty do you find works best?
Based on his description, I'm guessing B-3 means "Brown Stuff" and "Green Stuff", which are both two part putties, ultimately made by Polymeric Systems, but sold under a ton of other brands, at various prices. Green stuff, especially, is very common in the miniatures industry.
I usually hear Milliput referred to by it's brand name, rather than a color nickname. It seems to be less common. I am told, by reliable sources, that it has very different texture and working properties compared to green stuff. (I think Milliput is more crumbly, whereas GS tends to stick together and stretch or deform.)