Always been a potential problem, and still, despite the many years of existence of colour photocopying. I note than when Thais ask me for signed documents for officialdom they specify blue ink.
Edit: Forgot to add that someone will be along to say they have been filled in/signing everything in black ink for 30 years and never had a problem, but if you use black ink you might have a problem, whereas with blue they can't reject it on that.