Bright and Dark Cumulus Clouds

I noticed that some of the cumulus clouds today were producing light drizzles. Some of the cumulus were darker than others and this made me wonder if they had a different temperature than the brighter clouds. The visible and thermal images below indicate there may be a small amount of temperature difference. The brighter white portion of the background cloud is slightly darker in thermal infrared and therefore slightly higher.

Visible light image

A thermal image of the same cloud