Different panels have difference levels of gloss. The dash and steering column were originally a very very flat color, originally achieved through a special additive to the paint. Today, you can achieve a very similar effect by adding flatting additive to the same paint code. The reflection of the light off the flat, gloss, and semi-gloss will provide different shades accordingly.
Ok, back to the different pieces. The top and bottom of the doors, the trim around the back windows and such are gloss. The fastback side panels (if you have standard interior) are more of a semi-gloss as well as the pillar trim. (Deluxe interior has carpet on the side panels). The trim that runs over both doors are the same semi-flat as the pillar trim and rear side panels. Kick panels and steering wheels were molded in the original color, so if you need to color them, I would suggest just a touch of flatting additive to the gloss version of your red.
Your vinyl, whether your have the red seat covers and door panels, or white, will all be the same shade of vinyl. If you are ordering them, order a complete set at one time so they use the same run of vinyl. There are some variances as they make more.
I've tried to see if I had some photos of an original fastback with red interior, but I don't. I do have sample photos of other colors (blues, black, and burgundy like my car, etc.). Let me know if I can send you anything that may help.