Sprayed edges are page edges coloured after a book is bound, either in a single colour or in a stencilled pattern. They became a hallmark of modern special editions, especially subscription box editions and bookshop exclusives.
How to spot it
Close the book and look at the top, fore and bottom edges of the pages. Sprayed edges are coloured right across the edge, often with a pattern that continues around all three. Stencilled designs show motifs such as stars, flowers or symbols from the story. Some first printings of popular titles had sprayed edges as part of the trade edition, so check the edition details before assuming a copy is a special edition.
What it does to value
For collectors of modern special editions, the edges are part of what they are buying, and copies with clean, unfaded edges in their original box condition sell best. Rubbing, fading and dust on the edges lower appeal. Edges added later by a reseller are not the same as the publisher's or box's edition, and such copies sell for much less.
See special editions to tell FairyLoot, Illumicrate, Waterstones and deluxe editions apart, and limited and special editions.