Here is a simply way to figure out which colors in your palette are staining colors and which colors are easy to lift. Why is this something you may want to know ahead of time? If you are doing a painting and you make a mistake and you have a created this handy little chart you will know if you should go through the troubles of trying to lift the color out. Some colors do stain the paper and no matter how much time you spend lifting the color, it will not come out. Some colors will lift easily and you will be back to the white of the paper.
For this chart, I created about a 2 inch long swash of each color in my palette. I allowed the paint to completely dry. Then using an old brush and clean water, I scrubbed a small spot on each swatch. One color swash at a time, scrub with the old brush and clean water, blot with a clean dry tissue occasionally. This process can be repeated over and over on each individual color.
You will notice some colors have lifted out completely allowing the white of the paper to show again. Other colors are staining and no matter how many times you repeat the process, the color has sunk into and stained the paper.