In mine I keep track of all the paints I use and there company. Along with this I keep notes such as base coat, primary colors, shades, inks etc. And also the technique I used for application. Sometimes with even what brush size I used.
Now I know others have wrote about this in the past but if you haven't seen the articles or have never considered this I highly recommend it. Especially if you work on multiple projects at once or have more than 1 army.
Below is a picture of my current notebook along with the first page. Which is the one I have used for years for my romans and updated as paints have changed. This list I have used for about 4 years.
Anyway just a though for you all if you haven't done it already.