I admit the only yellow gold I really like is the 22k stuff from India and the like. I really am not a fan of yellow gold at all.
BUT look how I set Sunny. The yellow there even in a double bezel is barely there for me and it doesn't stand out much at all IMO.
If you want it to look yellow, get it partially set in yellow gold.
If you don't care if she pulls the rich pink color, then go with rose gold.
I am considering rose gold for my ring only because I am not looking for yellow again. I'm down to thinking of an L colored diamond so it could look fab in rose or just eh in rose. I need more time for myself.
I am lucky in that yellow gold doesn't look bad on me, but I just do not prefer it. My skin tone allows for quite a lot colors to look good on me.
It would be hard to pick between the two. The S-T is more rectangular but the Q-R would give more finger coverage even before a halo. The S-T while graded darker has strong blue fluor which might make it look less yellow in the sun. Lots of good to both really. I really think you can't go wrong with either though