Short answer: Adding more exterior and/or interior colors will increase the total no. of CX-5 combinations. I suspect more combinations in addition to the long overseas shipping distance would make it too unwieldy for Mazda to add more colors.
Long answer: There are 131 combinations for the 2019 CX-5. I had some spare time and just out of curiosity I calculated the total number of CX-5 combinations as an exercise in trivia:
Sport: 2 drive trains (fwd/awd), 2 option package choices (none/i-Activsense), 4 exterior/interior colors (red/black, silver/black, eternal blue/black, black/black).
Therefore there are 2 * 2 * 4 = 16 combinations for the Sport trim level.
Touring: 2 drive trains (fwd/awd), 2 option package choices (none/Preferred equipment), 12 exterior/interior colors (red/beige, red/black, grey/beige, grey/black, silver/black, eternal blue/black, deep blue/beige, deep blue/black, black/beige, black/black, white/beige, white/black).
Therefore there are 2 * 2 * 12 = 48 combinations for the Touring trim level.
Grand Touring: 2 drive trains (fwd/awd), 2 option package choices (none/Premium), 12 exterior/interior colors (red/beige, red/black, grey/beige, grey/black, silver/black, eternal blue/black, deep blue/beige, deep blue/black, black/beige, black/black, white/beige, white/black).
Therefore there are 2 * 2 * 12 = 48 combinations for the Grand Touring trim level.
Grand Touring Reserve: 1 drive train (awd), 12 exterior/interior colors (red/beige, red/black, grey/beige, grey/black, silver/black, eternal blue/black, deep blue/beige, deep blue/black, black/beige, black/black, white/beige, white/black).
Therefore there are 1 * 12 = 12 combinations for the Grand Touring Reserve trim level.
Signature: 1 drive train (awd), 7 exterior/interior colors (red/black, grey/black, silver/black, eternal blue/black, deep blue/black, black/black, white/black).
Therefore there are 1 * 7 = 7 combinations for the Signature trim level.
Therefore there are 16 (S) + 48 (T)+ 48 (GT) + 12 (GTR) + 7 (Sig) = 131 grand total combinations for the 2019 CX-5.
When you order a CX-5, your order is not sent to the assembly plant in Japan because its too far away. Instead you wait for a CX-5 to be driven off a cargo ship that matches the model year, trim level, drive train, option packages, and exterior/interior color that you selected.
Adding more color combinations could make it unwieldy for a smaller auto maker like Mazda. Im not a automotive production expert though. Because of the long overseas shipping distance, it would mean longer wait times if you want to wait for the dealer to get you exactly what you order. The 2019 CX-5 has 1-2 interior colors per exterior color. You can do the math like I did above and see what happens to the total no. of combinations by offering 3-4 interior colors for each exterior color instead of 1-2. Auto makers know that people are impatient for their new car to arrive and wont like longer waits.
If BMW and Acura are able to offer more color combinations for the X3 and RDX, it might be because both cars are assembled here in the U.S. unlike the CX-5.