I've skimmed the discussions in this thread and the same themes come up whenever disucssing colors. The consensus is that there are MANY different things to think about when matching colors.
Some of these factors include:
Finish (gloss vs. flat) Standards (FS 595) Scale Effect (reflectivity) Lighting (outdoors vs indoors) Fading (weathering) Paint Manufacturer
Here's a few things I've found useful for matching colors.
1) Use GE Reveal Lightbulbs: General Electric produces a new type of light bulb sold under the product name "Reveal". These bulbs create a light that is a "white" light as opposed to the yellowish light created by ordinary bulbs. This really makes a noticable difference in how the paint color looks in your basement workshop. They're a little more expensive but they're worth it and are readily available at most supermarkets and discount chain stores.2) Use a Color Wheel: I used to be scared to death of mixing colors because I had no idea how to do it. One of the guys in my IPMS chapter, who was a professional modeler, gave a lecture on mixing custom colors. He introduced us to a simple device called a Color Wheel that can be purchased in any art supply store for about $5. It graphically shows what the results of mixing colors are and how to lighten and darken colors. For example, to lighten a color, I always assumed that you would add white to it. But if you use the color wheel, you will see that adding white to red, for example, does NOT give you a lighter red, it gives you pink instead. By looking at the color wheel, you will see that adding yellow to red will give you a lighter shade of red. A color wheel is indispensible for mixing custom colors.
3) Lighten up: Unless you are building a 1/1 scale model of an item fresh off the assembly line, using the standard FS595-matched paints directly from the bottle will be too dark. Lighten the colors according to scale, lighten more the smaller the scale. Full-sized aircraft, for example, reflect a lot of light outdoors and appear lighter in color.4) If it looks right, it is: In the end, if you use the correct FS595 colors and the finished model does not look right, you've failed. The effect you want to go for, IMHO, is: "Wow! That looks exactly like the real thing!".
My $.02
Martin