Growing plants in food dyes does not alter the color of the plant.

This is because plants absorb water and nutrients through their root systems, which act as a sort of filter. While food dyes would not necessarily harm the plant, the roots do not recognize them as nutrients to take up, and thus exclude them from the plant. Thus, plants grown in dyes do not take on the dye's color.

However, you can see the effect of dyes on plants using cut flowers, such as those bought at the grocery store. These cut stems can take up water still through their stem, and when placed in dyed water will take up the dye along with the water since they lack the root's filtration system.

A simple experiment can be done with cut carnations in dyed water to observe the colored water moving up the stem and, with light color flowers and darker dyes, can change the color of the flowers as well.