I assume that since you have access to contrast paints you have access to other Citadel paints, and they have a few different "kinds" of paint pots. Youre already familiar with the contrast paints, but they also offer what is called "Base" paints and "Layer" paints, the type is printed on the pot. Ill add a picture. These are opaque paints that will cover any colour surface with enough layers of paint.
I dont know the exact differences between base and layer paints but base paints are usually more opaque and a little thicker, while layer paints can be a little more transparent and a little thinner, but it varies from colour to colour. Ive had thick layer paints and thin base paints.
Another brand is Vallejo, many people use their "Game color" range or the "Model color" range.
There is also a brand called The Army painter, but the truth is no one brand is better. I use all three of those brands for my painting, and there are even more brands that I have no experience with. As long as its acrylic paint, you should be able to paint a mini with it.
You should be able to just put another layer of primer over the mini.
A rule of thumb with contrast paint is that it can usually only make your mini darker, not brighter.