Originally Posted by Kristina9178
Other than mixing in white, is there a medium I can add to this transparent mix that will make it more opaque without compromising the color?
The "without compromising the color?" part is the main problem here Kristina. Basically the answer is no. studemobile has covered the medium types I was going to mention but fundamentally opacifiers will tend to alter colour slightly - acting like weak whites - and the more successful they are the more this will tend to happen. This kind of thing is
worth trying but personally I think it's better to work around the problem as a rule.
In the absence of an additive the two solutions are to mix the colour differently (from pigments that are more opaque) and failing that change the way you're painting that area, so that opacity isn't as critical.