https://future4200.com/t/gemstone-decarboxylation-sop/3354/5
There’s another related thread. See the research article i posted there as well.
4 hours is an incredibly long time for decarbing especially at those temps. Note what the article says happens to the CBD content over time. There is loss, probably isomerization but they didn’t pursue it to determine where the CBD mass went.
Are you doing it under vacuum i hope?
That blue/green looks like an azulene fraction. Search on the forum here and you’ll find several discussions on azulene.