I happen to be wearing a yellow shirt with gray pants today. Want a print of me for her quilt? LOL
Definitely ask for suggestions, then if you are lucky, you can go to a pattern you've been wanting to make that fits those suggestions. I made one a couple years ago where that worked nicely.

How about going to Pinterest and put in "grey, yellow and white quilts" and you can see many patterns to get ideas from. Good luck on your decision

I don't know how big of a project you are planning on... but I made my nephew a double wedding ring quilt in those colors. Not sure how my nephews feels about the quilt, but his new wife loves it :)

[ATTACH=CONFIG]596056[/ATTACH]

I did those colors in a Yellow Brick Road for a sister in law--turned out nicely

There are hundreds of patterns that use just 3 colors. Easiest out there are split rail, nine patch or a churn dash. If you can use various shades of the three colors, then log cabins would work. I think the better question is what style does she like? Is she traditional, 'old-fashioned' or more of a modern person? If she is modern, then an illusions quilt using white as the background, grey for the 'shadows' and a variety of yellows for the blocks would be outstanding!

I would suggest you take her shopping for fabrics for her quilt. That way she will be sure to like them, and you will have had a fun opportunity to bond over shopping and perhaps lunch after. Hugs and smiles... I look forward to seeing what you end up with!!

Perhaps you could spend sometime together on "pinterest" and ask what she likes then maybe narrow her choice to 2 or 3 and then it can be a surprise which one she ends up with.

[ATTACH=CONFIG]596093[/ATTACH]This is a disappearing 9 Patch that I made for a friend. The cream could be changed out for yellow.