So, when running vim under gnu screen and using a color scheme, some of the color sequences bleed into the prompt after I close the program. This only happens under gnu screen, and not when I'm not ...
open (vanilla) vim by running $ vim [-u NONE],
switch to insert mode by pressing a,
add an 'a' by pressing a again,
switch back to normal mode by pressing ESC, and
repeat steps 2 and 4 several ...