For a repaint on my '90 Miata, which is and will be red, I basically checked out vehicles I saw on the road for colour, hue, sheen, and light / dark depth. I would then write down the make / model / guesstimate of year and thus compiled a list of OEM paints that I would use for the repaint (as all body shops will have the paint codes and mixes, probably automated, available).
Eventually I came up with a "short list" of colours I was interested in. I followed up by visiting some local dealerships, taking a good look at the chosen coloured vehicles on the lot, and politely asking someone at the dealership to get me the paint code for the car or truck on the lot I had inspected.
The colour I decided upon was a Hundai / Kia code.
Why not a Mazda code? Firstly, I wanted something just slightly different than the OEM colour for the vehicle. It's old enough that modifications are worthwhile, something a little different or "custom" works for you with older vehicles, versus against you with newer ones. The Mazda colours are really quite nice, but they are all metallics for current and recent model years. i wanted solid colour paint.