Those aren't green stamens. It's a disfigurement of the rose bloom called proliferation. Some roses do it spontaneously, and some roses do it when you feed too much nitrogen, and some with a change in the weather that confuses them and makes them start a new bloom in the middle of the first one and before that one was finished. Back off the fertilizer for awhile and see what you get.

Kathy

Here is a link that might be useful: Pics of proliferation on HMF