In my experience I'd say far from cleanest while I've seen pictures online, between local show and tinley i've never seen a pure white Super russo, all had a yellow dorsal.
As for the BlkEL, the pink isn't a pigment, it blood showing through the white that is close to the skin. They have a lack of pigment so less is blocking it. When my blue eye baby hatched it was more pink than I could call white. Didn't take long for him to whiten up though.
The yellow from BlkEL stays, my super fire never lost or got more yellow as he grew up. If you are looking for pure white, I've never seen a super lemonback with color. If you like the yellow, super sulfurs tend to have tons of yellow and sometimes even oranges.