video on composition.  there's 3 parts, but you only have to watch the first section to understand about space and contrast, and apply it to photos (esp. lifestyle)

https://www.youtube.com/watch?v=1McYZX6KScg&list=UUbdyjrrJAjDIACjCsjAGFAA

Site for color theory, very sciency.  Important parts to note are Describing Color, How we See Color, Color Memory, and Color Fatigue

http://www.graphics.com/article-old/color-theory-fundamentals-digital-photography