Wondering if anyone else has come across this. Periodically, I'll open the camera app and the preview will be dark blue for a second and then switch to a black preview with no image showing. If I switch to the video mode, the correct image will appear on the screen, sometimes continuing to work if I switch to the photo setting again, sometimes just going back to a black screen once I switch. Sometimes it takes a restart to fix the issue, other times a lock and unlock seems to do the trick.
I believe others have posted on this issue. I personally would have the iPhone replaced.