One way to try to get the right color is to use a Pantone color guide (usually found on eBay). Once a match is found then make the trip to the craft store and get the matching color. Another method involves mixing your own colors by adding a few drops of the tint you need and then adding either a few drops of white or black to lighten or darken. Do this on a small sheet of glass so that you can lay it on the playfield to see how close the natch is. When creating these color "samples" write down how many drops of each color so that you can recreate the color later.

Although I've used the mixing method I found it tedious and somewhat difficult to get a decent match across many colors. I find using the Pantone color guide has worked very well for me and primarily stick to it now.