In the "Custom Order Note Box simply list up to 5 colors that you choose from the Flake Color Chart located on the Color Chart Tab page. There is no extra charge for custom colors and you can order the flakes to ship separately instead of mixed so you can experiment with different color ratios. Plus ArmorGarage has a Color Satisfaction Guarantee. If your not happy with the colors of the flakes when you receive them will replace them with another set of your choosing at no cost! As for why we don't have a simulator, we feel the results you see don't match reality and more often than not it leads to disappointment. Best to look at our customer pictures for the best representations.