This might sound a little crazy but bear with me.
When a thought type becomes a supertype to another type, the type display list popup changes so that the subtype appears, indented, beneath the supertype. For example, say we start off with types A, B, C, D, E; they appear on the popup list (reading downwards) as A, B, C, D, E. If we now make D a supertype of A, the list changes to B,C,D,A,E, with A appearing below D and indented, demonstrating A's inheritance from D. Likewise, if E becomes a supertype to D, the list order changes to B,C,E,D,A, A and D being successively indented compared with E.
First let me say it is very nice to be able to see the relationships between types and supertypes set out clearly like this; it makes understanding supertypes so much easier. However, on occasions this can be a handicap, particularly when one has 30+ types and several supertypes.
I have two reasons for using supertypes. The first is to collect subtypes under one umbrella so that instead of filtering for types A1, A2 and A3 in Reports, one need only filter for type AA, where AA is a supertype to A1-A3. Here the indented supertype hierarchy looks good and I guess was meant to serve this purpose. In this example, the types list reads (downwards) ... AA, A1, A2, A3, ... , with the supertype at the head of the list.
The second is to use supertypes for holding colors (or icons) for subtypes. When PB beginners suddenly discover the power of coloring a type so that the color of all thoughts assigned to it can be switched by making a single change to the type's color, it becomes natural to keep colors where they belong, in an assigned type. However, the number of usable colors is finite and relatively small compared to the number of types that might be useful, especially across a collection of Brains.
I run about half a dozen Brains, using a core set of about 20 types with the same names such as Important, Keyword, Miscellaneous, Priority (red color), Web page, Job, etc., for each Brain. Tags are ok too, but I don't display tag hints and prefer the thought's color to tell me its purpose. In most cases I can maintain the same color scheme across all the Brains, but occasionally when a particular Brain requires extra types I find myself having to make compromises with colors, so that the type Keyword which might be light blue in one Brain has to be made light green in another as the light blue was taken some time back and changing it requires changing the colors of half a dozen other interrelated types.
This would be no problem at all if I assigned all colors to supertypes. Then, type A1 would inherit its color from supertype Magenta, type A2 from supertype LightBlue, etc. Sample thoughts each named after a type or supertype could be pasted into each Brain from a central source, with types already included and dependencies set up. Then if it turned out that LightBlue was already a supertype of C1, A2 could also share that color if I didn't mind two thoughts with the same color, or if I did, it would be a simple matter to make A2 inherit its color from supertype LightGreen. No fiddling with the color disk required. These colors are already preset.
With this scheme, color supertypes are better off hidden at the very bottom of the types list so that they don't interfere with the grouping of types. However, I haven't found any way to turn off the indented supertype display which puts LightBlue above A2 in the list. If there is no way to disable this feature, is it worth suggesting this to the developers?
(added) Just to make this clearer, I would then rename the supertypes zLightBlue, zMagenta, so that alphabetically they sink to the bottom of the types list. I access supertypes much less frequently than types, anyway.