Ubuntu 16.04: How to turn off colors in terminal?

Open up the hidden .bashrc file in your home and comment out (add a # to the start of the line) all lines relating to colour in that file.

Save a copy first just in case it all goes wrong so you can restore the original if necessary.

I like a colour prompt and output in my terminal so have never tried this but the main one for the prompt is shown below (line 43 in my file but may be different line in yours.)

Line to comment out to stop colour prompt:-
force_color_prompt=yes
so it becomes
#force_color_prompt=yes