Theme colors not working in Ansi256

[jphager2]

Describe the bug
Text colors do not work as intended in Ansi256

To Reproduce
Steps to reproduce the behavior:

1. Use Ansi256 Terminal (e.g. Mac terminal with Settings > Profile > Advanced > Declare terminal as: xterm-256color
2. Configure colors in ~/.typer.yaml like:

theme:
  bar:
    color: '#555555'
  graph:
    color: purple
    height: 3
  text:
    error:
      foreground: '#FF00000'
      background: '#FFFFFF'
    typed:
      foreground: '#0000FF'
    untyped:
      foreground: '#555555'

3. run typer

Expected behavior
The configured colors should be approximated for the terminal.

Screenshots
If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

• OS: [e.g. iOS]
• Version [e.g. 22]

Additional context
I think that the termenv color profile should be used when setting the colors. Will make a PR for this. (Also termenv has had several version changes, and could be updated. Happy to do that if desired.)