When The Sibley Guide to Birds first appeared the colors were criticized. In particular the brightness of certain rufous colors (e.g. Brown Thrasher) and blue colors (e.g. Jays), which seem too intense, and some gray species (e.g. gulls) which appear too bluish. Efforts to correct this are ongoing, but the process is not as simple as just “taking out some blue ink” or “darkening the rufous areas”, and will almost certainly involve retouching original art and rescanning selected paintings (much of the trouble is with the original art). People often ask me if I am happy with the colors in the book, and I certainly am. The original paintings are rather bright, showing the birds at their best, brightest, and most contrasting, as if on a sunny day. The reduction and printing enhanced the colors throughout, creating a rich, bright look to the whole book, and in a few cases pushing the colors beyond the range of normal. When looking at the colors in the book bear in mind that our color perceptions of birds are controlled by lighting: a Brown Thrasher in sunlight looks much brighter than one in shadow, and there is of course no practical way to show such variation in a book. Similarly, the colors in the book itself appear to change under different lighting conditions, compare the appearance of the pages under fluorescent light with that under sunlight.
Maps generated the most criticism, and I suppose rightly so. The attempt to show migration routes and vagrant records on a small field guide map was, in my opinion, successful, but many people pointed out that the green dots showing vagrant records are often not placed accurately. My intention was simply to show the broad pattern of such records for a given species, rather than details of individual records. In that sense the system works, but I agree that the dots imply a kind of precision that is lacking in the actual maps. These maps were reviewed by experts from every state and provice, and completely revised maps are now published in the Sibley Field Guides to Eastern and Western Birds (the original maps are still in all printings of the Sibley Guide to Birds).