Need Help Tinting

I am going to paint a Case SC with SherKem enamel, and have already bought 3 gallons of an orange which seemed to match the original color (Flambeau Red). I used the SherKem color selector chart to match the paint chips with several original samples, in various light conditions, and it seemed to match very closely. However, the paint chips on the cans seem to be too light.
The labels on the cans seem to display the formula for the color as a mixture of a stock red, a stock gold, and white. Therefore, I got out the Testors model paints and began mixing. I found that I could get both the color I wanted and the color on top of the cans, and the difference seemed to be the white. It only seemed to take a touch of white and red, and a lot of gold.
Unfortunately, I can't remove the white from the paint. However, I think that I can add more untinted "pure color" (just the gold and red mixed in the same ratio as indicated on the cans) to the mix. Is this a valid approach, or will I have to buy a whole lot of "pure color" to get it to untint, since there us so little white in the original mix? I don't really want to buy 6 gallons of paint in order to correct an issue with 3 gallons of paint.

I'm not sure what color tint they use for the SherKem enamel. Your Sherwin Williams manager should know and be able to get the red pigment needed to alter the paint. More than likely the red color tint in their machines isn't colorfast enough for what you are doing. Red is the color most likely to fade so you need to be sure you get the right one. If they alter the finish be sure to keep the formula for posterity.

forget the "chip" on the can and put some on a part and let it dry and then compare it. Make sure you actually have a problem first.

I went to the Sherwin Williams store and talked to one of the workers there. He gave me about 14 fl. oz. of red tinting pigment and 2 fl. oz. of gold tinting pigment. I then took some measurements, ran some calculations, and mixed paint samples using the pigment and pipette tubes. I now have 5 paint samples with concentrations of red pigment increasing from 1X to 2X the original concentration, and 4 paint samples with concentrations of the proper red/gold mix in the same ratios (I didn't bother with the lowest ratio for this mix). I can now compare my samples and back-calculate the number of fl. oz. that is necessary for the new tint. I want to wait until the paint hardens for a few days before scuffing some of the paint on each sample, since I scuffed all of my original samples to remove the oxidation.
I am also thinking about going with a little extra red in the paint to compensate for the fade over time. Does this sound like a decent idea?