How high can the humidity be generally for blush free spraying? Think spray can paint, not retarder laced dope.

I didn't think it mattered from a rattle can until one model turned white. Guess the paint can pick up plenty of moisture in a foot of travel and drying time. 

Also surprised to find that it was a problem with enamel, not just laquer.

We live and learn! Now to learn what I need to know. 

Randolph recommends under 50% if you care about blush.

Their retarder (a slow-drying thinner) helps reduce blush if you can't wait. 

How high can the humidity be generally for blush free spraying? Think spray can paint, not retarder laced dope.

I think it would vary widely by brand.  Someone that routinely sells into humid areas might put retarder into the mix, to prevent blushing.  Someone who routinely sells into dry areas might make a fast-dry mix, either for economy or to reduce drying time for the consumer.

You're kind of at the mercy of the paint supplier.  I'd try looking at their web site to see if they have recommendations, but I wouldn't stake my enjoyment of life on finding an answer.

I have a barometer in my shop. I've shot as high as 70% without problems, but you are in the range at that point. Generally anything above 60% without retarder or at least extra thinner is going to be a problem. When it gets on toward 80% (which it is a lot around here), you can hit it with retarder and extra thinner and cross your fingers. It might be OK. Maybe. Anything above that and it's just not worth it.