Smithsonian Institution
Smithsonian American Art Museum: John Whorf
As part of the Smithsonian Art Museum's database of artists, John Whorf is described here along with information on his contributions to art through his work as a watercolor painter.
ClassFlow
Class Flow: Composition Color
[Free Registration/Login Required] This flipchart discusses the characteristics of Georgia O'Keefe's paintings and provides some web links for Georgia O'Keefe's work.
Smithsonian Institution
Smithsonian American Art Museum: Adolf Dehn
As part of the Smithsonian Art Museum's database of artists, Adolf Dehn is described here along with information on his contributions to art through his work with watercolors (including his three books on the subject).
Art Institute of Chicago
Art Institute of Chicago: Watercolor Paints
See an example of watercolor paints in this image and description of the painting medium.
Other
Create a Mood With Color Key
Clearly defines high and low key color pallets. Provides visual examples and links to other color concepts. Attention is directed to watercolor painting, but can be applied to other painting methods.