Color is my "thing" and I ADORE mixing paint colors to create new colors!!!

I used whatever we had leftover from our house paint to create new colors for DD's dollhouse. She chose some colors "as is", but mostly I mixed up existing paints to create a whole new set of colors.
Just last weekend, I was cropping (scrapbook-crafts) at a friend's house and she wanted to delve into paint for the first time. I only had one color with me of paper paint (bright orange), so I dug through her craft paints and found another color (dull medium pink). I mixed them together and the result was PERFECT for what she wanted.
Without seeing the colors, I couldn't advise you specifically. I do all my color mixing on instinct and they always turn out great.
In general, decide if you want light or dark. Mix any colors first, then add white to lighten (if desired). Mix enough at the beginning because you can never match it exactly once you start. If I know I want one color, but just don't have quite enough.... I use that one color as the base and add little bits of other colors into it....stirring a LOT and then stirring even more....until I have enough paint but before destroying the original color (unless I like the results, then I just keep going). If I want a brand new color, then I start mixing in a clean container (5-gallon or paint tray) using equal portions of the colors I have at hand first and then altering the portions as I see what develops. I generally get the color right first and then adjust the value (lightness/darkness) with white, gray, or black. It just works faster for me that way.
Without seeing your exact colors, I would say the green and gray-blue might go well together and the peach and white will look good together. If you needed more volume than any two of those, you could probably get away with adding little bits of the opposite colors if you are just a bit shy on volume. The green, blue-gray, and white might work, but the white might also wash out those colors. Try a little bit in a baby food jar first and seal it tight for a day or two while you deliberate.