Intensity:  For light shining through a colored solution,the observed intensity of the color is found to be dependent on both the thickness of the absorbing layer (pathlength) and the concentration of the colored species.
For One Color:  A series of solutions of a single color demonstrates the effect of either concentration or pathlength, depending on how it is viewed.
Side view
Top view
(a.k.a. BirdÕs eye view)
Visual Colorimetry