Like you, I had an IBM PC in need of paint restoration. I used the Pantone 413 suggestion and the result.... drum roll please:
Repainted PC on left, factory PC on right.
TL;DR (my experience)
My PC unfortunately had large areas where rust had completely eaten away the original paint to the point that it was not save-able (pic, pic). I was able to remove the rust and to preserve as much texture as possible, sanding lightly only to even out spots before paint. It was never my intention to make this PC perfect either in an "in the past" or "historical" sense. I have two others that are in better condition so the objective was to make this one presentable. Nothing much to lose here.
I ordered two spray cans of Pantone 413 U from myperfectcolor.com. A family member who is a professional graphic artist suggested using the 413 U (uncoated) rather than 413 C (coated) since the color would look less saturated and more true.
I used a sandable gray automotive primer to cover the exposed metal area and lightly sanded to remove only the most uneven parts. I then applied several light coats of the 413 U paint, allowing each to dry for 24-36 hours with very light sanding in between. After the last coat had fully cured, I applied a light even coat of paste wax as a protectant.
As you can see it doesn't look exactly like the other. This isn't necessarily a bad thing - it still looks nice. There are numerous reasons why this would be of course, and here is an incomplete list that come to mind:
- The original paint has aged and changed color.
- The original paint is of a different chemical formulation than what I purchased.
- The underlying primer I used was a different type/color.
- Pantone 413 C might have been more accurate than 413 U.
- Variations of factory paint formulation, process or color over production span.
- The original color wasn't exactly Pantone 413.
- Any, all or none of the above.
It's certainly not simple to find an old reference photo of a brand new PC from the 1980's that's accurately colored. Many online photos are scanned faded magazines, advertisements or digital photographs in various lighting conditions where the colors can appear to range anywhere between the these two.
I do have another PC with original finish in addition to the one in this picture and the color is pretty consistent with the one on the factory finish (right). Also notable is that darker keys on the keyboard are much closer in color tone to the factory PC. Not sure that dyed plastic would change color over time in the exact same way as metal but who knows. FWIW, these PCs were stored for the last 25 years or so in a light-free environment (a dark attic, then a dark basement) so at least weren't subject to a lifetime of UV.
Anyway, thought I'd share my experience having done what the OP asked with the hope that it might be helpful for someone someday.