Not sure to which you refer but unless it's organic green leaves or green powder it's processed chemicals... If it's white powder or clear liquid it's dangerous and processed - quite possibly carcinogenic
The green stuff has a distinct taste of slight bitterness, the white or clear stuff has had the sweeter aspect enhanced via processing, and the bitter taste this reduced.
Stevia isn't suited to everyone's pallet. It needs other stuff to help jazz it up. Green stevia on oatmeal will be hard to do without other things to cover the "green" taste.