Bloom

The Blue Pearmain runs to deep red. The apple gets its name from a dusty blue bloom it often wears.(Photo: 

Blue Pearmain) 

Many apples bloom, not just the Blue Pearmain.

A bloom is just an excess of the natural wax that apples exude, some more than others. It is fragile and wipes off easily.

Or, you can eat it.  I've never noticed any taste from a bloom.

An apple's waxy cuticle layer, the outermost part of the peel, repels water and protects the fruit. It's about a fifth of the thickness of a human hair.

Some apples produce a little extra of this natural wax. That is the bloom.

Notes

You might see a bloom on fresh apples at a farmers market or orchard. Not in a supermarket: it will have been rubbed away. Other waxes or lacquers may have been applied.

You can take a closer look at cuticle wax, courtesy of the USDA's electron microscope.

Bloomin' McShay. Both photos show how easily the fragile bloom can be scraped or rubbed off from normal light handling.