Printed with no issues and looks good! I know my green isn’t quite right but close enough…also used the orange glow in the dark PLA for the orange sections. Thanks!
Go through the usual steps of extruding the entire model. Hide everything so only the sketch is showing. Highlight the entire sketch then deselect the perimeter wall. Extrude it at -0.2, in the Start drop menu change it to Object. Ensure the operation is set to New Body. Then flip the model so you're viewing the back, Unhide any colour and click on the now visible colour. This will create the new body. Lable the new body as Diffuser and add it to your other White bodies/components.