I'm trying to add a color adjustment to a strip in the VSE and got that working fine, but I'd like it to fade in and out rather than hard stops and when I add the cross or gamma cross, it just fades to black rather than to the strip below it. I've tried playing with the settings (add, subtract, alpha over, etc.) but none of those do what I'd like it to. I have successfully done crosses between regular strips and to color strips so I'm fairly certain I'm doing it correctly, but the adjustment layer is hanging me up. Is there something different I need to do for an adjustment layer?
You can animate Opacity value of Adjustment strip, for creating nice fade effect.
How to animate values:
Select Adjustment strip and in the N-tab find Opacity value.
Set time where you want to fade start, hover mouse cursor over the Opacity value and press I
Set time to the end of fade, set Opacity value to 0 and press I again, while hovering cursor over the Opacity value