Well, medium palomino is one of the colors you can't get, so this is how you'd have had to do it anyway. Get the conversion spray and medium palomino spray and make the black one right for your car. Cleaning of the repro is the most critical step, I use a detergent, then a degreaser, then a solvent paint cleaner, all scrubbed with a Scotch-brite pad. Then the conversion spray, finally the interior color. Set the pad on a piece of plywood so you can spray it all at once, instead of having to flip it over.
Don't do black, the palomino interior is rare and special.
When I did my soft IP (as well as all the hard trim), I went to the local automotive paint store and got what I needed. They sold me a can of plastic prep (residue free) and some color matched SEM paint (SEM is the manufacturer of the paint, not a paint type - just to be clear). I painted it all with a regular spray gun.
I also took a black 1969 center console and painted it dark red to match my interior. I have had no issues with the soft armrest or any other part of it.
You can manipulate the gloss by the thickness of the coating. I wanted the IP to be slightly more glossy than the trim so I put on thicker coats.
the SEMs products come in a spray can and work very well. I did all the soft pieces in my 68 so that they would be the same shade of red.
The SEMs products are a three part system - cleaner, prep, color. Follow the directions on each can. Spray the color coat immediately after spraying the prep BUT on that first coat spray the color from about 2 feet away so that it dries before it hits the surface. Spray on a VERY light coat - just enough to cover lightly.
Then spray on several (I do about 8) VERY LIGHT coats of color. Let it dry between each coat (it dries very quickly).
Did I mention to use VERY LIGHT coats of color? You do not want to fill in the grain.