OK - not sure if this is going to help because the lighting in the picture may not show true. For starters, I use Nick Maglieri's recipe for SMBC. 5 whites + 1 1/2C sugar + pinch salt + 1 lb butter. Proceed with usual SMBC technique.
But....while the whites were beating in the stand mixer, I beat the butter in a separate bowl till it was fluffy and it did look less yellow.
When it was time, I added the butter in scoops and beat until the frosting was the correct consistency. I didn't add any flavors 'cause I'm freezing these batches and Nick M. says don't flavor till you're going to use it.
Well.....it looks a little
bit better - I thought it was pretty good till I used a piece of white paper to compare. I think when I go to use it, I'll try lorimom's suggestion - I'd heard once before about adding a color, but couldn't remember what it was.
The top half of the picture attached shows the frosting in containrs on my (white with small speckley pattern) counters - the bottom half has a piece of white paper to compare.
HTH a little!