Hey, I had a similar issue.
I wanted a Jetblau R8 4.2, like this one below:
BUT... with the carbon thingy on the sides. And the carbon thingy is only available with the Eissilber Metallic color:
So I bought the very car in the screenshot above. Then I went ahead and bought another one in Jetblau (exactly as in the first picture, with the silver thingies on the sides).
Next step would be using the Jetblau paint chip for the first R8.
WOULD. Neither the 4.2 or the 5.2 add the paint chips to the inventory.
This is how the actual color looks like in the game:
A bit "grayer" than what it should actually be, but anyway. I started to look for the color. Tried suggestions from this topic. Tried several, took the car to the track, it looked weird under sun light. Not even close to the real car in Jetblau.
Came up with this one:
Suzuki Alto Lapin Turbo 2002, "Lake Blue Metallic"
Result below:
At first i thought "meh, another fail" since it didn't really looked like the original color.
But when I took it to the track...
It is exactly what I expected.
Sometimes the desired color does NOT show very accurately in the car dealership (or interface-rendered pictures)...
I guess I was lucky to find such a cheap car as this Suzuki as the one to deliver what I wanted.
I hope it's what you expected too, or at least close to it.