I personally would do it in one of two ways:
- I would make the black text a lighter grey (something like
#CCCCCC
or#DDDDDD
- I would make the background a little lighter (again, something like
#CCCCCC
or#BBBBBB
could work here)
If you are a designer of command line utilities, you could also say "well, this is for the UX guys to solve". The fact is though, that somebody has to do it, and if you don't have a UX team or you are working alone, then it's up to you, even if this means fixing accessibility issues that the terminals themselves have.
Obviously, you can disregard this (accessibility is underestimated way too often), but if you can focus on it, kudos for that. The fact that you asked this question is already a good sign.