If Amazon.com cannot locate a book you are looking for, you can search for the title yourself on the Internet, using any major search engine. Personally, I found two of the following out-of-print books, Colors from the Earth, and Color in Art: A Tribute to Arthur Pope at abebooks.com, a network of independent booksellers. If you cannot find these books anywhere else, they may be available at your local library, and if not in their collection, your library may be able to obtain a copy for you on interlibrary loan, which can give you access to books in public and University libraries throughout a large area.

On colour psychology, Max Lüscher is the acknowledged expert here (do you kind of get the idea the Germans have colour theory sewn up?...with the exception of Chevreul, of course). He has created a deep psychological test based on colour choices in a controlled setting, and has also worked as a consultant for industry regarding psychologically appropriate uses of colour. His book is called:

The Principles of Harmony and Contrast of Colors, by M.E. Chevreul [Special Order], is an important book, both historically and theoretically. Chevreul, when he took over the Gobelins dye and tapestry works, found a number of problems in the weaving were really colour problems, mainly to do with how colours affected each other when juxtaposed. This is a very important work on simultaneous contrast, and also deals, necessary, with that kind of colour mixture that is neither additive, like light, nor subtractive, like pigment, but is called "medial," and has to do with colour mixtures in the eye.

For insights on colour vision and perception, I highly recommend:
Colour and Colour Theories (Classics in Psychology), by Dr. Christine Ladd-Franklin [Special Order] or, for special edition with library binding.
Dr. Ladd-Franklin developed her own theory of colour vision with none of the weaknesses of either the Young-Helmholz or the Hering theories, and squares with the witness of perception (for example, a man colour blind in one eye who wrote about his perceptions, and who is ignored by the other theorists, because what he saw was not what they predicted, fits perfectly with Ladd-Franklin). To understand this book, you need to understand something about the way coloured light mixes. This is different from the way pigments mix, but since many readers will be thinking of applications for the web, coloured light mixing (additive colour) will be more relevant to you than coloured pigment mixing (subtractive colour).

For a more practical book on techniques for taking advantage of colour perception:

Color Perception in Art [PB, Special Order], by Faber Birren. This book, along with Johannes Itten's book, and the first book I mentioned by Birren, can give you lots of ideas about how to get the results you want in the brain of the viewer.

For a discussion of the way lights and pigments function, the following book is serviceable:

Lights and pigments : colour principles for artists, by Roy Osborne; Unknown Binding (HB, Out of Print); there is also a PB edition.

A rather obscure book, but one with something new to add is the following:

Color in Art: a tribute to Arthur Pope, James M. Carpenter (Fogg Art Museum, Harvard University, 1974) (PB, Out of Print). Arthur Pope's colour solid has two interesting features: he takes into account the fact that each colour, at its brightest and purest, is naturally a different value (lightness or darkness), so pure yellow is the lightest, pure violet the darkest. Lots of theorists gloss over this. He also divides his solid at yellow, not red, which I think is more satisfactory, for many reasons. This is worth looking at, if you can get it on interlibrary loan somewhere. While I cannot find it in any current listings, there is one book by Pope which may give some illumination on his ideas on art: The Language of Drawing and Painting, although this one is also out of print, it appears to be more "gettable."

Further along the idea of the effect colour has on people medically, and not just psychologically, is the following:

The Ancient Art of Color Therapy: Updated, Including Gem Therapy, Auras, and Amulets , by Linda Clark (HB, Out of Print). Some of the things in this book veer into the realm of psychic traditions and practices, but they are recorded relatively objectively, and the medical discussions are enlightening, even if one would hope for further studies to be done on what is essentially a folk-medicine tradition. I find this dovetails quite well with the psychology of colour. Use this link for the PB edition.

Regarding Art History, we go back to Faber Birren again, with the following title:

History of Color in Painting by Faber Birren (HB, Out of Print). This book discusses the colour palettes of various eras of artists with great specificity. This book is also out of print.

The following books are very useful to painters:

Artists' Pigments c. 1600-1835, by R.D. Harley (HB, Out of Print). This is the most complete book I have seen on the manufacture and use of artist's pigments, and clarifies many problems with nomenclature that are inevitable as people constantly call different things by the same name, and the same thing by different names. The illustrations from sample-books are also fascinating. While Harley's focus is on this specific period, there is much information about the pigments before this time.

The Materials and Techniques of Painting, with a Supplement on Color Theory, by Kurt Wehlte (Van Nostrand Reinhold, 1975) (HB, Out of Print). An exceedingly thorough study of painting materials, including pigments and colour theory, by a theorist with practical experience in painting and teaching. The author was held captive by the Russians in the second world war, and made to test oil paints made with the oil of a special variety of sunflower seed. He heard, twenty years later, that the samples were still bright as the day he painted them. Use the following link for the PB edition.

Controlled Painting: A sound approach to realistic painting in oil and acrylics, by Frank Covino (PB, Out of Print). This book puts into practice some of the colour scales from light to dark first found in Faber Birren. Another edition of this book.

Colors from the Earth,
The Artist's Guide to Collecting, Preparing, and Using Them
by Anne Wall Thomas (HB, Out of Print)
This book, in a few short pages (96 pp.) covers what earth colours a person can find, their history, their modern use, their preparation as pigments, and how they can be used in oils, egg tempera, pastels, and printing inks. The directions have clear instruction with photos, and there is a useful glossary at the back. This is the only book I have ever seen that directly addresses the question of an artist wanting to make and use their own earth colours.

This should keep anyone going for quite some time. I have been reading books on colour for many years, so I have tried to hit the highlights in this list. Have fun!