How to send to front/back ("z-order") when editing an image in Preview I have added an oval to an image in Preview and would like to either send it to back or change its transparency:



Well maybe the transparency were asking too much of Preview  - but the others?



Why are they disabled?  Is there a way to get the oval to not blot out the area it covers?

Update: Attempt to set transparency:



Note: the oval has become completely invisible now: the blue dots show the location of the timid object:
To make it transparent, open the color picker on the very right, and chose the white square with the red line through it.



The other options are disabled because there is no object underneath/above it to send behind/in front of. The image itself you are editing does not count as an object.