The original, unused Ditko cover for Amazing Fantasy #15 has been published by Marvel at least twice over the years, and in both cases the black & white artwork was coloured. The version on the left is from
Spider-Man Classics; the one on the right is from a later publication,
The Official Marvel Index To The Amazing Spider-Man.
The one on the right, the newer one, looks "better" to my eyes ~ more "plausible" colouring for the most part, except maybe the purple building! ~ but I'm wondering if an "official" version of the colour guide for this cover was ever made in the first place? Are one of these images accurate, or are they both just guesses at what Steve and Stan intended the colours to be?
(Does anyone have a large scan of the original black & white art?)