Patches, you mean patches on the glass?
Usually people like that colorful addition. Most of it is beneficial algae. Some people introduce algae purposely in their tank. For example, Coralline Algae.
Or there is the other case. When you see a solid "nasty" color taking up most the glass walls its a algae bloom. Most likely diatoms. In those cases, it usually good to control it by buying a cheap magnetic glass cleaner. It comes off easily. Its also great to check your water, reduce daylight hours or other methods depending upon your specific problem and what other inhabitants you already have in the tank.