What feature distinguishes the X-Ray Tetra from many other tetras sharing its habitat regarding pigmentation?

Answer

A lack of opacity contrasting with relatives that use dense pigmentation

This species exhibits a striking lack of opacity, which contrasts sharply with many other tetras in the same habitat that rely on dense silver, red, or black pigmentation.

What feature distinguishes the X-Ray Tetra from many other tetras sharing its habitat regarding pigmentation?
locationhabitatanimalfishTetra