why does absorbance of light increase as the concentration of dissolved food dye in a solution increases?

Due to the fact that the dissolved food dye molecules in the solution absorbed a certain color of light, the supplementary color (the color not absorbed) observed is the color of the solution.

As the concentration of dissolved food dye, there is a greater number of food dye molecules to absorb the certain light per unit volume. In other words, the absorbance of light increases.