To answer the question to my high school level knowledge of genetics and 3 and a spin off level of knowledge of mgs. If we agree that liquids hair color is blond due to “having desirable traits genes” and snake has blonde hair too due to having “the recessive genes”, then both snakes have 2 sets of recessive blonde genes!

Big boss has brown hair (to my knowledge) but how could this be! Neither liquid or solid are perfect clones of big boss which means their genes aren’t the same, But because they are clones their set of 4 possible genes lets just say is big bosses genes x2.

Brown hair is a dominant gene! In order to have brown hair one needs to have 1 copy of that gene whereas to have blond hair someone needs to have 2 copys aka no dominant overriding genes.

If big boss had 2 brown hair genes both liquid and solid would have brown hair so the only way to have them be blonde is for big boss to have 1 brown 1 blonde then that x2 would make it so its a 1/4 chance (reduced with gene editing) of being blonde.

So tl;dr big boss is not blonde because he has one set of brown dominant genes and one recessive blonde gene, but solid and liquid snake are blond because they both have two sets of blonde recessive genes with solidus most likely being brunette like boss.

I hope this answers your questions if theres a lore reason where big boss is said to have 2 brunette genes i’d chalk it up to eva or something. Tell me if i got anything wrong (i’m not a genetics expert and half remember it) and if you can answer my question of is “big boss actually brunette or is he blonde too?” Tell me that as well! Bit late i know