Are these 3000k lights? If so, you're probably knocking around the additives that change it from a 5000k light to a 3000k light. My understanding is that the additives are used to make flourescent lights appear more "incandescent" in nature (i.e., yellow). There are also expensive additives in some lights to increase the CRI (color rendition index) number.
I'm just wondering if you're not seeing the "true color" when you give it a smack.