Just a heads up
I tried the Uchida red and Y&C fabricmate red pens on the back of the passenger seat but they both came out looking magenta. In some lighting it actually looked pinkish.. At least to my eyes.
So I went over it with the Elmer's red (which I didn't want to use since its just a paint pen and not a dye pen) and it looks tons better. I'm sure it will fade in the higher traffic areas of the seats but I'll just reapply. Just try it out in an inconspicuous area before you dive in.
I didn't think to take a picture of the magenta but here's the Elmer's:
It looks a little orange in the pic on my monitor but it really is quite red.