All I could think of is red goes well with gray. Please take a look at the idea photo.

A warm white.

there is so many options with grey. Grey goes very well also with green, white, turquoise, black, purple. There are fantastic combinations of two or three of these colours. It depends on your taste.

and yellow of course!

Being an art teacher, I'm always reminding myself of the color theories like this one : look at the gray you've got. Is it a yellow gray, a blue gray, a green gray, etc. whichever it is, pick the color opposite on the color wheel to pop next to it. So if its a greenish gray, then a red would be the color that pops next to it, a blue gray, it would be an orange.