I did a very quick and dirty job in Pixelmator Pro with the yellow iMac. The iMac is, of course, not to scale, and the perspective and color shading is totally inaccurate, but it might be a bit useful—not really sure. My suggestion would be, given that all of your furniture is white, I think that any color you want would complement your space well. I think having a nice, vibrant, bold iMac would really add pop to your space, so don't shy away from a cool color. More white would be pretty bland, I think.