Printing VT20 / VT30 on coloured paper

Spoke to VOSA today about using coloured paper for VT20 / VT30. - NO WAY will VOSA allow it. The guy then went into a long speel about the printers being set up for white copy paper only, I stopped him in the end and said OK we'll continue to use white paper. I did point out that it doesn't say anywhere in the manuals you must use white paper !