How can you tell???

[nice_corals]

How can you tell the difference from an onyx and a reg true perc???

 

[Speg]

Onyx has much larger areas of black.

 

[ficklefins]

From what I understand:
The black in the onyx will follow through the body and actually make contact with all three white bands. But I'm not sure if there is anything more that you have to look for.