You can change how colors are mapped to file types (when you color by "File type" via the Display tab) by editing the Uniform Type ranking, accessible from the GrandPerspective menu. You do so by changing the order of the file types. Each file is mapped to a color by determining the first file type in the list that the file conforms to. The order of file types is important for two reasons:

• Many files conform to more than one file type: one specific file type, and possibly one or more general types. The order therefore determines which of these types is used to color the file. For example, if the public.jpeg type appears below the more general public.image type then JPEG images will be assigned the same color as other image files. If, on the other hand, the public.jpeg type appears above the public.image type, then JPEG images will be colored differently from other image files.
• The number of available colors is typically smaller than the number of file types. It is therefore not always possible to assign each type its own color. Only the types at the top of the list may be assigned their own color. Types lower down may all be mapped to the last color that represents all other file types.

If a file type appears in the list below a (more general) file type that it conforms to, it is "hidden" because it will never be used (the more general file type will always be assigned to any file that also conforms to the more specific file type). Hidden file types are indicated in light gray.

The Move to reveal button will move a hidden file type upwards in the list so that it is above all file types that it conforms to. The result is that the file type is now actively used by the color map. Similarly, the Move to hide button moves an active file downwards in the list so that it is below a type that it conforms to (or at the bottom of the list, in case it does not conform to any type). Hiding a file type means that it is not used in the color map anymore.

The Move to top and Move to bottom buttons can be used to respectively move a file type to the top or bottom of the list. The Move up and Move down buttons can be used to move a file type up or down by one position in the list. Alternatively, you can use Drag and Drop to change the order of file types in the list.