Blue buzzers do have their day, as does probably any colour! I am certain that blue suggests the air bubbles as they ascend to hatch.
Perhaps since New Year it has been too cold for many buzzers to hatch and therefore, bloodworm imitations may have been better - fished slow and deep. Smaller flies may have been the key.
Now the water has warmed a little, and therefore a few more buzzerd hatching, the blue, irridescent patterns may be more likely to take a few fish.
This is the fun of fishing - experimenting and then trying to find out why something works (or doesn't

)