What does the density potential (also known as the electrostatic potential) measure? What do

the colors on the images indicate?

Since this is not my area of expertise, I searched Google under the key words "density electrostatic potential" to get these possible sources:

http://www.elmhurst.edu/~chm/vchembook/211elecpotential.html
http://www.cgl.ucsf.edu/chimera/docs/UsersGuide/filetypes.html
http://books.google.com/books?id=ega5c11VHvkC&pg=PA164&lpg=PA164&dq=density+electrostatic+potential&source=web&ots=tM0qVU8Bzl&sig=pBuJkVIC8OQSWhuuyXYpFGwHkNA&hl=en
http://www3.interscience.wiley.com/cgi-bin/abstract/114188940/ABSTRACT?CRETRY=1&SRETRY=0
http://www.canby.com/hemphill/chmimg.html

In the future, you can find the information you desire more quickly, if you use appropriate key words to do your own search.

I hope this helps. Thanks for asking.