We have an application in which users carry out similar tasks on different types of reports. As such, the user's first interaction with the app is to select a Report Type. To make it easy to tell at a glance which type they're working on, each one is associated with a colour, which becomes the dominant colour in the UI whilst working on that type.
So, for example, Foo Reports use blue; the icon for selecting the Foo category is blue, the background becomes blue when working on Foo Reports, and many UI elements are drawn in shades of blue.
Bar Reports, on the other hand, use Red. Baz Reports use Yellow, etc.
This has been a successful approach for a half-dozen or so different types. But the number of report types is climbing over time, and we are naturally running out of colours which are easy to differentiate from one another.
How can we manage the profusion of different colours while keeping the UI usable? Failing that, what would be a minimally-confusing way to move away from this scheme?