I believe you will be able to mix primary latex paints. If you go to get the
paints mixed, maybe they will show you the tinting formulas for the colors you
choose so you can see just how primary they are, and predict how well they will
I've mixed student grade acrylics from tubes into latex paint to get new
colors, so that might be another option for extending your acrylics.
My preference for "primaries" are cyan, magenta and yellow- kids can mix red
with this and can get a purple that isn't muddy or dark.