When a Layer is filled with color and a Mesh object is on the same layer in transform mode,
How to move the object in canvass Z axis pushing it behind or in front of the color?
Ye olde Z way:
“T” “W” (brings up axis gizmo) LM outside of the canvass area and the object moves in the canvass Z axis.
As far as I know, it’s still the same as it has been for a long time. Draw your object on the canvas, switch to Move mode (W), then LMB+drag up and down on canvas.
You can also activate the gyro in Move mode, then use Transform>Info>Z to set a specific depth.
Or before you draw your object on the canvas you can set Picker>Z to the desired depth.
I believe there are technical reasons (to do with the implementation of perspective) that the model in Edit mode will snap back to zero Z Depth, whatever you set it to using the gyro.
The Image Plane plugin is designed to overcome some of these difficulties.