In addition to its trend forecasting reports and focus on consumer habits, WGSN also features a color library of nearly 30,000 color swatches from Pantone, Coloro, Archroma Color Atlas, and more. Click on "Colour Library" under "Design Resources" in Fashion or Interiors to access (CCS credentials required).
You can also design custom palettes using "Colour Play" in the bottom menu - you must be signed in to your free account in order to access it.
Luna is the image database for CCS; see the links below for images related to color (CCS credentials required):
Color Theorists: Itten, Albers, et al.
Tonalism and Monochrome
MIX Magazine, from Colour Hive, provides access to color and materials forecasting information, available both online (CCS credentials required) and in print.