It would be good if not every negatively charged protein would be 100% blue and every positively charged would be 100% orange but they would have different strong tones of the color based on the numerical value of there charge.

There should also be a mode that shows the charge based on the current status in the protein.
A histidine can sometimes be charged positively and sometimes be negative depending on the surrounding animo acids and it's not easy to determine it as user at the moment.