I understand the inhibit cue and I think it's a great idea. But the problem I see is that it will only allow you to fade a single colour in/out. As soon as you change colour by recalling another palette it will go straight to full on stage, regardless of the position of the inhibit fader. You could not fade one colour out, select a new one and fade that in. So I'm not sure how useful it really is (apart from with chases).
To fade shapes (recorded in cues) you can toggle size and/or speed between static and fading via softkeys in [Shape Generator]/[Playback Parameters]. You can then either set a timed fade on the playback in mode 1 or by fader in mode 2. ie. set size to timed and then set playback to mode 2 for manually fading a shape in/out by fader.
Regarding the zero palette IIRC the attribute banks act as a mask when recording as well as when recalling. So before recording the palette make sure the attribute is set to either dimmer (include all) or colour.
Also, from your detail of palette recall I wonder if you realise you can record palettes to the grey preset keys? In 'Run' mode these flash the fixture but in 'Run Takeover' (and program) they are palettes. If you enable 'palette paging' in User Settings you can have four pages of palettes which change with the fixture page buttons. And by enabling 'quick palettes' you can even recall without having to select any fixtures (although the option to filter by selection still remains). Finally, unless you have more than one attribute type stored in a particular palette you can also leave the mask set to dimmer and not worry about selecting an attribute bank either.
This means that if you want you can recall a palette with a single button press which will not enter the programmer and so not require clearing. For timed recall simply input time (in seconds) on the numeric pad before selecting a palette.
Because you only need three channel RGB personalities there are actually loads of HTP versions in the library including
ColorBlast 12. Unfortunately it does look like the LTP and HTP versions have exactly the same name in the console, which isn't very helpful. Alternatives include Generic RGB HTP, Pulsar ChromaFixture Single Cell HTP and the majority of the James Thomas fixtures.