The fact that you're asking this has me a little worried...lol
They're supposed to turn red, it's some what of an indicator as to when your buds are ready to harvest. Not THE indicator, but a hint. The true indicator is the trichomes.
From the GrowFAQ:
Harvest timing is a matter of personal preference. When the glandular trichomes are clear with very little, if any coloration, THC levels are at their peak with CBD and CBN both at levels that will not overly influence the THC with their sedative effects. Some prefer more overwhelming narcotic type effects, allowing the resin glands to cloud and begin to amber or darken to increase overall cannabinoid content. The resin glands appear and therefore will mature at different times. A compromise is made when determining the desired overall maturity level to harvest. It depends on the growers preference in effect and palate.