What's the recommended temperature for chocolate to set? I have been making various kinds of chocolate bonbons for about 8 months with great success. (Once I had mastered tempering, that is.)

I had read somewhere (but I can't remember the source) that chocolate that's allowed to set in the fridge will not set with the desired crystal structure, even if it was properly tempered, so I normally leave it on a kitchen counter overnight to set. In winter it worked very well, but these past weeks we have had serious summer heat, and the kitchen has been above 25°C, and the past couple of times my chocolate has ended up rather grayish and out of temper.

The last time I tried to let it set in the fridge, and it looks better. It's got the right gloss, but I'm not 100% sure that it has the same snap as I'm used to. 

What is the recommended temperature for properly tempered chocolate to set?
The recommended temperature is 20°C. This is 12 to 13 degrees Celsius difference to the actual chocolate temperature. 1-2 degrees deviation will not be a problem, but more than that and you will get subpar results. 

This temperature should ideally be the same on all sides of the new chocolate shape. This means, if you are covering something in chocolate, you also have to balance the temperature of the surrounding air, the covered thing ("core"), and the chocolate. In this case, you also ideally have 20° covered thing, 20° air and 33° chocolate. But if you really have a deviation, you should try to at least have air and core at the same temperature, so 22-33-22 is better than 18-33-22. 

I also once wrote an answer which adds detail from an article on tempering truffle couverture, you can find it at this question.