Actually "warming -> melting ice -> less reflection of sun -> less heat" would go other way around. If you have light surface it's likely that lot's of visible light is radiated to space. If you have blue sea instead it's likely it radiates only infra red. Which would be bad with elevated CO2 levels.

The most believable negative feedback I have seen is about increased cloud coverage. Clouds should then reflect visible light back to space. At the same time water vapor is the most significant greenhouse gas in the atmosphere. We really don't know how it's going to turn out.