I started having some fun with V8 yesterday and found this.
There is quite a difference between these two display modes in V7 to V8 of Rhino.
Same model, Isocurves are turned on on both of them. There are no special files for the background.
Below is V7
And Here is V8
It successfully reverts the custom display mode settings all the way back to Shaded. It is simply a copy of the Shaded display mode.
On the plus side, the Cplane is now fixed.
may need to remake your custom mode for v8, lots of display changes under the hood.
Hmm, ok I am tracking. Thanks 
This is an old bug, sad to see still exists:
Notice the grid still showing, even though should be off.
The workaround is to choose ‘grid ontop of objects’ rather than ‘transparent’:
The bug seems to be worse in other display modes, like ‘arctic’. I think there’s another thread on it.
Additionally, I like to make these colors brighter:
I wish they were already that way by default 
Well, I’m noticing a conflict now though, with the axes not being ontop of objects unless ‘grid is transparent’ 
I better go check V7… brb.
Ok so in V7 I have it working somehow…
transparent plane no, transparent grid yes … brb
Yeah idk, the bug looks worse in the WIP:
Maybe if the grid and the axes had separate transparency parameters, then there’d be a workaround with that, and maybe if the scaling were separate or if the axes scale could be more than 100%, then there’d be a way to trick it, but nope…
Yeah it’s looking more like a V8 WIP bug on every display mode now the more I look at it:
pretty sure this was mentioned recently in another thread, on arctic display mode, but I couldn’t find it…
This might be the one I was thinking of:
