#544 Rolling Fog is not "super super light gray". #11 Snow White is the lightest gray though warmer in color than #544 Rolling Fog (you'd think, based on it's name, that #11 Snow White was pure white; it's not, pure white is #381 Bright White).

If you're at Home Depot or another store that sells CM grout, you might want to look at the sample grout sticks they have rather than relying on the paper brochure (which I did).

super light gray? Mapei, Warm Gray. I used it w/mine

try a diff grout manufacturer if you can't find what you like

this other shower was done in Oyster gray by Custom Products