I haven't used iPhoto on our white MacBook running Lion for years. I did so recently and I discovered I was afflicted by the Photo turns black while editing bug.
At first if I clicked the 'enhance' button the image vanished to be replaced by an all white icon. If I click Shadow or some other edit controls it went entirely black.
I upgraded to the very latest version of iPhoto (9.4.2) and repaired permissions/repaired database (cmd-opt-start). Now I have exactly this behavior:
... I am using a MB core 2 Duo at 2.16 MHz with 4 MB RAM with MacOS 10.7.4 and iPhoto '11 (ver 9.3.2) and have a problem with editing photos when I change the 'shadow or highlights'. The photo turns to black when I move the slider off the zero mark and the photo returns when I move the slider back to zero.
I had the same problem with the previous version iPhoto ('09 I think) and bought the new version '11 to try to fix the problem. The problem seemed to go away for a while but has returned. I have tried starting iPhoto using command/option and repairing the permissions, then rebuilding the thumbnails, then repair the database and then finally rebuilding the database. Each time I tried a repair, I tested the shadow/highlight edits and got the same black result. All other adjustments work fine. It is just the shadow/highlight adjustment that turns everything black ...
I moved the problematic library to my primary machine and, unsurprisingly, there were no problems at all. I think there's a bug in iPhoto that renders it incompatible with my old MacBook's video processor. Apple is very unlikely to fix this.
Update: Aperture on the same old MacBook has no problems. If I adjust shadow in Aperture however, the image is all black in iPhoto.
This is a bug that affects rendering of at least some JPEGs following shadow/highlight edits on MacBook Duo with integrated Intel GPU.