That doesn't mean you only wear one color. It means that 'contrast' pieces can be used with a number of existing items. Also plan for flexibility in usage. When you plan to buy a blouse or shirt stop and ask if it will work well with a number of suits and slacks. If it doesn't go with things that are already in your closet, you're committing to making another purchase to go with the first.
Flexibility is a key to keeping a wardrobe 'fresh'.
Also, when it's time to dispose of an old item you haven't destroyed an entire outfit. The other items are still useable with other matches. Yes, it's possible to dress in stylish quality for less. It takes a little education and effort. This book is the best on saving on your grocery bill.