Check out the webpage of the Computational Vision Lab at Simon Fraser University http://www.cs.sfu.ca/~colour/. It has links to other researchers' web pages as well. You should know that there has been a lot of argument against Land's theory. For example the paper: Brainard, D.H. and Wandell, B.A. (1986). Analysis of the retinex theory of color vision. Journal of the Optical Society of America A, 3, 1651-1661. Reprinted in Physics-based Vision - Principles and Practice, edited by Lawrence B. Wolff, Steven A. Shafer and Glenn E. Healey (1992). There has also been a lot of work on color constancy, which is what retinex claims to do. For the colour constancy work, my lab page (http://www.cs.sfu.ca/~funt/) is as good as any to start from. You should also look for more recent papers by my ex-student, Graham Finlayson, in the Color Imaging Conference proceedings.