Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.
There isn't any toolbar to change line/pencil color.
How to add the toolbar?
I have installed Kolourpaint from default Ubuntu repositories.
Right click the Menubar (File Edit View ...) and enable the "Color Box"
Required, but never shown