One way to quantize colors is to use a photo editing program. Using the color picker tool you can read the RGB values of any color. Paint a sample of your mix, let it dry, and scan it with your scanner. Open that image in your scanner, then examine the paint area of the image with the color picker tool. To speed things up, you can put down several test mixes, scan an image of several blobs of different mix, and look at each blob. Now the tricky thing is, most colors mix using subtractive colors (magenta, cyan). So, you need to read up on color theory (lots of good articles online- try google). I believe some of the better photo editing programs may even convert to yellow-cyan-magenta as an option.