Can I re-process homemade applesauce canned in a boiling water canner that is too thick and pasty?
The simple answer is yes you can re-process. Follow standard processing procedure for applesauce once you get your applesauce to the taste and consistency you want. (Personally I like very thick applesauce.)

You said Maybe I didn't heat it hot enough before canning, since it was so thick. Did you bring it to boiling before putting it in the jars? If it was not hot at the time of packing you could possibly have a safety issue, depending on how long the jars were in the water bath. 
The applesauce being thick is only a canning/safety issue if there are large trapped air bubbles in the jar.

The color of the applesauce is not an indication of a problem. If you used tart apples they just didn't oxidize much. If you want to change the color you could add a bit of cinnamon. (it is possible it will darken up a little on it's own over time)