Remove hard coded color in shell exec

[skbolton]

aichat/src/main.rs

Line 264 in 0493134

let command = color_text(eval_str.trim(), nu_ansi_term::Color::Rgb(255, 165, 0));

I use the shell assistant all the time and really appreciate the feature. Unfortunately the hard coded color that is currently in use goes really poorly with my theme and doesn't present itself that well. I wonder if it would be possible to use the yellow color from the terminal env vs a hardcoded value.