Centruroides bicolor and gracilis comparison

[MarkNaja]

Hello all,

So I have a question about these species and can't really find an answer.
I have bicolor (i4) and gracilis (i4) and wondering how is the best way to determine which is which. I see many similarities, I can tell when they are adults but for this size, is there a giveaway that I cannot see?

 

[Veno Manus]

Gracilis have dark black or dark redish/brown telson. Bicolor have tan and black.