I had the same problem and what turned out to be the problem was an app called Twilight that automatically "warms" the tone of the display at dusk. As robs246 mentioned, it appears that it's apps like this that automatically adjust the display that can be the culprit. For me, if I disabled that app, the install button worked, and when I re-enabled it I could no longer install non-Market apps. Strange, but at least I found the problem. Samsung Galaxy S3