Hi Joseph. The nominate ensicauda larvae from those newts are a lighter shade of brown, while my popei larvae are dark brown to black:
(nominate ensicauda)
(popei)
I think the larvae of my other nominate ensicauda, the ones that don't have this special coloration, are a bit darker, but I'd have to check...
Good luck with your popei larvae
Thanks, Carlos. The tank is 90cmx45cmx45cm.