@Phil Mckerracher @kgallen
So, after testing this on both v7.14 and v8 I have shown that...
You don't seem to be able to alter defaults on a Solution showfile - even when it is loaded on an FLX running the FLX-only v8 and been saved on that and reloaded. This seems so wrong that I fear it may be me and the way I am doing it. If it isn't then it probably warrants a call to support.
You can achieve default colour black by making amended copies of fixture personalities.
Fixtures with a default of white behave exactly as I would expect (i.e. the reverse of what you and I would like). They start with white and, as the playback is raised, they fade out the colours that are not needed.
Fixtures with a default of black, on the other hand do what I expected and would like and also what I suspect you need. These start at black and fade up the colours needed.
Where another playback is already up the (default white) fixtures, the behaviour of the both black- and white-default fixtures is to raise the "missing" colours and the lower the "unwanted" ones effectively replacing the original PB's colour with the new one. T would seem to be the required behaviour but contrasts with faders set up for colour mixing. If you want to mix playbacks then you should refer to the instructions for this in the manual.
My recommendation for you achieve the look you require is to set a default of black fr LEDs in your showfile. While this does not seem to be possible through changing the fixture defaults you can do it by creating modified fixture personality files and replacing the library ones in the patch.
However there is another way - one which use all the time. On an FLX I use a multi-function key (latched and with release disabled). I save all the default values I need for a show onto this. Not just default colour black but things like stair edge lights at 50% and default positions for moving heads. I engage this when I start the desk up and record the "default" values I need for that day's show on to it. These values would, of course, be restored whenever that show file is loaded. As you do not have MFKs you could use instead. You might find it helpful to disable raise-on-lower on this PB. Be careful about recording HTP levels on this as they will become the minimum level for those fixtures and you will not be able to go below it. For our stair lights this is, of course, exactly the behaviour I require.
Hopefully, this, and the various bits I have sent you by DM wi help you to achieve the reults you require. Have fn!