What paint color to mixed to make paint color lighter?

The answer is white.

However, yellow might be added to a color as well to make it lighter, but it might change the original color. Also, when you add white to a color it is called "tinting" the color. When you make a color darker by adding black, it is called "shading". Shading is also a technique in drawing. Be careful not to try shading and tinting because the result is the color is "grayed", by adding black and then white you cannot reverse the effects of the black, only change the effect. I hope this helped!!