If I was God trying to show my existence in an appropriate matter, I would not just rely on experiences given.
People need to understand the other side of the coin:
Example: Try telling me why God exists...but first, tell me why you think God exists. Can you actually justify to yourself enough evidence? Dave needs to realize that maybe he cannot justify even himself color does not exist which is another perspective to look at.
I am not saying that since Dave is color blind that is enough. I am saying Dave needs more. Like a court case...you don't win by one small piece of evidence, you need a well rounded argument to prove it well.
In the same way, I feel religious people have done a terrible job at doing that which is why a) most consider God a fairy tale and b) tons fall away each year from religion.