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Answers : They brown ones are the same species as regular brown and albino bristlenose plecos, except they are longfin. They are the same species, just different coloring due to genetics.
The tips usually stay white, they just get a little faded. Meaning right now, they are nice and bright white, but when fully grown, they turn to an off white. The longfin ones will have more prominent white when fully grown because they have longer fins than the regular short fin. If you look at the short fins, they have a sliver of white on their tail too.
My brown bristlenoses do not have brown parents, they are spawns from longfin albino parents. Therefore, if you end up getting a male / female, you will have a good chance of getting a whole bunch of albino babies. =)