Today, colour printing is industry standard. It makes sense to use colour in your printed material when you consider the following:

People are 80% more likely to remember what they read if it is in full colour
Colour also helps executives locate information 70% faster
Colour marketing materials leave a 39% more memorable impression
People are 55% more likely to pick up a full colour mailer first
People are 85% more likely to buy a product promoted full colour
Colour even helps invoices get paid up to 30% faster

However, this is not to downplay the importance of standard black and white printing. Black and white, when used appropriately, has its niche and its purpose.