Kaleidoscope is a third party theme manager for System 7 and Mac OS 8, written by Arlo Rose and Greg Landweber.

It utilizes a proprietary framework to apply "schemes" to the Macintosh GUI, long before Apple released the Appearance Manager system with Mac OS 8 (later updated in Mac OS 8.5, providing similar functionality using "themes").

[1] When theme support in the Appearance Control Panel was first announced, the team responsible for it demonstrated an automatic tool specifically designed to convert existing Kaleidoscope scheme files into Appearance Manager-compatible theme files.

Steve Jobs returned to Apple just before the release of Mac OS 8.5, and he officially discontinued support for themes in order to force a consistent user interface.

As a result, Kaleidoscope schemes proliferated while Appearance themes never really did.