If you need to quickly change the color of some latex house paint, you can do it by adding artist's acrylic paint. The reason you can do this is that latex paint is really just a type of acrylic paint, so it is compatible with artist's acrylic paint. You can use acrylic paints just like commercial tints, adding it to your house paint to change the color. The easiest way is to use fluid acrylics, which you can just stir into the house paint. Fluid acrylics, though, are less common and more expensive than tube acrylics. To mix tube acrylic paint to latex takes an extra few steps to ensure complete blending.
Squeeze out the acrylic paint into the cup. Start with a small amount. You may add more at a later time if needed. If you are mixing a composite color (two or more colors) put them into the cup together.
Swirl the paint in the cup. Use the brush or stick to blend it and spread it around.
Add a few tablespoons of water. You don't need a lot. The principle is to soften the paint and make it more liquid.
Mix well with the stick or brush. Uniform color and viscosity is the goal.
Pour the mixture into the latex paint. Stir vigorously. Keep mixing until every trace of the streaks of acrylic paint are gone. Ladle up paint from the bottom to see if there are unmixed traces. When the paint color is totally consistent, it's ready for application.