On my 1968 El Camino the paint code is G2. The G is half of normal size. The color was Grecain Green when I stripped it to bare metal. So did some one mess up at the Factory?

For clarification, is your question, why does the cowl tag show a "G" (Gold) instead of the an "H" (Grecian Green) when the paint was obviously green?

I've seen paint codes where the second character is a number before. In my experience it indicates a vinyl top. Code 2 is black.

In '68 the General used a single paint code "letter". They switched to dual numbers in '69.
If you are saying the cowl tag said "G2" to the left of the word "paint", those stand for the Lower and Upper Body color. So, yes, I agree with lcamino that the "G" is for Ash Gold Metalic. But my opinion is that the "2" stands for a Lower Body color.
I would think the vinyl top would be either a code of "AA" for white or "BB" for black.

That is just how I'm reading it and is only my opinion.

But I guess your real question is why was the green on there right above the metal??

The truck has a black vinyl top so the 2 makes sense. When I got it it was gold but the last color before metal was clearly Green. It was even on the firewall that had never be repainted.