What do stores accept as coupons printed off a coupon site?

Has anybody used coupons that you print off from coupon sites for products? If so; when given to the cashier at the check out, do they have to be coloured ink or could it black ink? Do they have to be printed on white paper? I have only black ink at the moment and a whole box a green computer paper to use up.

What is a VPN?

VPN is (Virtual Private Network) were first used by companies to enable their employees to securely access internal systems such as email remotely (e.g. from home or while on business trips). Today they are increasingly being used for personal use by individuals to protect their privacy while online in public places (e.g. when using the wi-fi connection in a cafe) or in a country where the internet is censored / blocked (e.g. China, Saudi Arabia��).