I'm not really fond of the ID sebae, as there are 2 types of sebae, and they are dramatically different in needs, size, colors.
I would guess though, purple/blue tip would most likely be a crispa, foot in sand at base of rock, loves lots of light, pretty good flow, gets very big and will reach high for light.
Malu on the other hand, total sand dwellar, medium light and flow, stays low at bottom usually, much smaller(8-10" as opposed to 24") and can come in very bright colors.
I don't think either are really difficult to keep as long as healthy and given proper conditions.