The Solitary Vireo has bold white spectacles and more conspicuous wing bars than the Gray Vireo. The Bell's Vireo has a dark eyeline and lacks a complete eye ring. The Hutton's Vireo also lacks a complete eye ring. Both Hutton's and Bell's Vireos are more olive than the Gray Vireo.
Length and wingspan from: Robbins, C.S., Bruun, B., Zim, H.S., (1966). Birds of North America. New York: Western Publishing Company, Inc.