Know Your Medium
I want to stress the importance of knowing your medium.
While working on a portrait I needed to fix some errors. The paper was off white, so I would have to make my own correction fluid to color match the paper.
The plan is to mix a brown with white until the color is as close as possible. I have two colors of brown, Burnt Umber and Sepia. One is warm and the other is cool.
When mixing them with the white I discovered that the Sepia turned grey! Not what I was expecting. I quickly abandon the idea of using the Sepia. Now I know that if I need a toned grey I can use it.
The Burnt Umber mixed well and gave me the correct tone I needed for the paper.
Below is the swatch tests I did.
You can see the differences in color.
Not all browns are the same.