Hi Skinny !
Imagine a compo displacing and colorizing a plane with two Sphere Mask:
If you want to share the same Sphere mask for the two 3d modifiers, you just have to right click on one of the two Sphere, and made it shared. This by clicking on the "Share Element" menu of the Sphere of the Colorize mask for instance:
The shared sphere mask name will appear with double bracket. This mean that the mask here is a shared reference of a Shared Element.
The Shared Element will appears on top of the Compo. You can [control]+drag it into the Displace mask to create another reference of it and delete the old Sphere contained by the displace mask.
That's all !
I hope this will helps.
The best.
