This species, like some other heron species, displays an unusual, non-sexual dimorphism, with some members having entirely white plumage and others (the larger portion) being grey. The reason for the colour variation or "morph", is unknown, though it is most commonly thought to be related to camouflage.
White morph Pacific Reef Egrets are very similar to Chinese Egrets. The main differences are:
1. The Pacific Reef Egret has noticeably shorter legs than the Chinese Egret;
2. In Chinese Egret the eyes are set noticeably above the gape; in Pacific Reef Egret they appear lower and closer to the bill;
3. The Chinese Egret has a dagger-like bill while Pacific Reef Egret has a more droopy-like shape and the upper mandible sometimes appears to overlap the lower mandible at the tip.

First 4 photos: Dark morph. Tub Kaek Beach area, Krabi, Thailand, 4 February 2013
Last photo: White morph, in the company of a Whimbrel. Klong Muang beach area, Krabi, Thailand, 20 January 2013

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