The range of colors that GoodNotes offers is amazing, but it can be difficult in practice to fluidly incorporate them into documents. This could be streamlined considerably by having a coloring tool that allows the user to change the color of pen and highlighter marks by stroking over them with their pencil.

Motivation:
There are a lot of use cases where it is useful to have multi-colored diagrams and writing. For example, is often helpful to color certain variables and subscripts in mathematical equations to intuitively link equations together. As it is, doing this either requires changing the pen color up to a dozen times while writing a single equation, or using the lasso tool to edit the color of each stroke afterward.

There are a couple of problems that using the lasso tool for coloring runs into:
1. The biggest is that the lasso tool can only select so small of an area, which makes selecting individual strokes (e.g. subscripts) hard or impossible on large pages.
2. The lasso tool also takes a considerable amount of time to use. This is in part because of the point above, but also because for each stroke that you want to change, you have to select it and then tap twice to get the color that you want.

When using two or more colors, and/or selecting multiple small elements, this can make the process take quite a long time. In my experience, this means that I often forgo using the coloring options that GoodNotes has available, as doing so during or before a lecture/meeting is too cumbersome of a process.

This could potentially be incorporated into the lasso tool as a 'mode', which might also allow changes to line thickness, or an option to keep it or the color unchanged. It would probably be cleanest from a UX perspective to create another tool, though I could understand an apprehension toward adding another tool to the suite.