To follow up on this, a regular 4' bulb, 4100K is about $6-7 at Lowe's. The same bulb in a 6500/6700K which might be better for plants would be $15-25 at a LFS or Petsmart/Petco.
So, if you're growing plants or it's a display (only?) tank, then it's probably worth getting a bulb that will enhance colors as well as improve plant growth. If it's for a bunch of tanks in a back room, I just run regular bulbs on those - no plants, and while I want to see the fish, coloration is not as essential...at least not worth 2-3x the cost to replace all the bulbs.