The Dan Lanning era kicked (literaly since they only scored a FG) off with this all-apple green combo against a dominant Georgia in Atlanta. Being a special kickoff game the teams went color-on-color. It was like Christmas (but no gifts for the Ducks) in September!
The yellow facemasks appear to be a new addition to the green helmets, as I can't find any green helmets in Duck history with yellow facemasks. And the only yellow mask on non-yellow helmet I could find was 2016 with black helmet and angry duck decal.
They last went mono-apple green in last year's game against Oregon State. Their most famous use of this combo was in the Mariota Rose Bowl victory against Florida State in 2015.