Unless your Mac is being slowed by heavy processor load, a slow internet connection, etc., the condition you describe is not normal. Disconnect your Mac from the internet, restart, and test Photo Booth again.
In addition to the suggestions CMCSK has offered, consider whether you have multiple apps open when you try to use Photo Booth. Perhaps other running apps are connected to your iSight? Perhaps your Mac merely needs an unusual amount of time to switch between many apps while continuing to support processor demands of other apps you are also running? When looking for other apps, be sure to consider "Widgets" in your Mac's Dashboard or "Login Items" in > System Preferences... > Users & Groups.
If your Photo Booth green symptom occurs immediately following a restart with no other apps running and no interent connection, ask your Apple Care Service Provider to check your Mac ASAP. It may need to be serviced or exchanged for one that works properly.