Configurable colors for auto prompt mode

**Is your feature request related to a problem? Please describe.**

Found the auto prompt mode when looking for a solution to the aws-shell v2 cli problem. Looks great, but the contrast of the panels is nearly unreadable in my terminal.

**Describe the solution you'd like**
Either use different/safer (0 - 15) colors or make it configurable

**Additional context**
I am using [base16-shell](https://github.com/chriskempson/base16-shell) to set my terminal colors (including 16 - 21) with the [tomorrow-night](https://github.com/chriskempson/base16-tomorrow-scheme) theme.