Why they keep lightened up the skin of the gods?? Not accurate

This is papyrus of Hunefer. May be this picture above is not the best quality photo of this papyrus, but anyway, in this papyrus the Netjeru have light-brown skin color - neither white, nor dark black.
You may see the official webpage of British Museum highlighting this artifact:
http://www.britishmuseum.org/explore/highlights/highlight_objects/aes/p/page_from_the_book_of_the_dead.aspx