how can I disable colored output when hitting ruby warnings and errors?

ruby 2.7.2 on linux

I run ruby in a way that creates error messages. Part of the messages come out white which, on the very light xterm background I'm using, is unintelligable. Example...

% /usr/bin/env ruby design_parser.rbTraceback (most recent call last):        1: from design_parser.rb:175:in `<main>'design_parser.rb:175:in `read': No such file or directory ... blah...blah... (Errno::ENOENT) 

The "Traceback" and the last line are white, I can't read them, have to cp/paste them somewhere to see what they are saying. Very annoying.

Looked for but did not find anything from 'ruby -h' to shut the coloring off.

Can this be done ?