Re: How can I reduce the effect of sugar blush, over time, in candy?

You might try eliminating the corn syrup.

Retrogradation of starches (which causes staling of bread) squeezes out 
water, which may show up as a sugar crystallization problem. Corn syrup 
solids contain considerable dextrins and starches.

You might also examine the moisture content of your candy. If too much 
moisture remains, it will evaporate out and be re-adsorbed due to 
temperature fluctuations, ruining the surface consistency of the candy.

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Admin note:

Mukund V. Karwe adds the following:

Try adding some glycerol.  That acts as a humectant (keeps moisture)
therefore recrystallization does not occur, or slows down.

-MVK