Interstingly enough I don't get any devide by zero errors, but that may just be because WebGL errors are caught and abstracted by the browser enviroment. I guess that is why we never see them. 

For any soldid color we have the case min=max for each channel. The result is always a black image. I don't know what to return in this case? The defaults (all min = 0 and all max = 1)?