IMO, Genetics is way more complicated than we like to portray it. Labels like hypomelanism are used accross species lines with ZERO knowledge as to weather the actual genetic mutation is identical, similar or completely different. All we know is the outcome visually is somewhat comparable.
Prime example is the two "albino" strains in BCI, Kahl and Sharp. Both look very similar, both are a form of albinism, but are totally incompatible with each other.
As to why the trait expresses how it does - dunno. To me it appears very different then "hypo" in BCI. In BCI Hypo visually appears to replace some of the black with red. In BRB, the black appears to be gone along with some (if not all) of the red leaving yellows and browns.
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Thanks,
Dave Colling

www.rainbows-r-us-reptiles.com
0.1 Wife (WC and still very fiesty)
0.2 kids (CBB, a big part of our selective breeding program)
LOL, to many snakes to list, last count:
26.49 BRB
20.21 BCI
And those are only the breeders 
lots.lots.lots feeder mice and rats 

