"You can add commercially available universal pigments up to about 8 fluid ounces per gallon.
Looks like one can order their paint and custom mix your colors.
Now if we can just find the pigments..."
Hi David, I'm responding to your post and quote above.
Universal pigments will mix with water-based, oil-based and lacquer-based coatings.
The really good news is that they are easy to obtain.
These are the pigments that are in all of the pigment dispensing machines in all the paint and DIY stores.
I have been using these pigments for years to color my dope and with black, white, red, blue and yellow, I can cook up any color I need for my scale models.
Take some small bottles (I use 2 oz dope bottles) to your paint store and have them squirt what you need into them. This stuff is concentrated

so it doesn't take much to do the job.
Since they usually don't sell pigments this way, they may seem reluctant to help you so throw yourself on their mercy and tell them what you need it for and they will usually figure out what to charge you; you may even get it for free

if you have just purchased all the paint you need for the house!
Orv.