Blueberry flower buds are starting to swell.  Some varieties (Blueray) are wine red before they open; they turn white like all the rest when fully open.

The blueberry flowers are still closed and leaf buds are starting to emerge.  Flower buds at this stage are protected to about 26 F.

Why don't blueberries ripen all at the same time? All flowers don't open a the same time; nor are they pollinated at the same time.
This is a sample plant during a good bloom (2010).  Not all flowers are ready to be pollinated but will be over a 2 week period.
Click here for other photos of flowers being pollinated.
Notice the small amount of frost damage.  Yes, it did frost the night of Thunder over Louisville (4-17-10).

The photo on the left shows development in all stages.  Some flowers are closed, some open and a few have been pollinated.  You can notice 3 (four if you count the one on the left) stigmas attached to the  blueberry in the callyx cup stage.  The photo on the right shows blueberries in callyx cup stage but most of the stigmas have fallen off.  Some frost damage is apparent but it is not significant.