It probably doesn't help the plant grow to have the extra food coloring present, but it does not hurt either.
In theory, the food coloring should have no effect on how the plant grows. But because of what's called "capillary action," the food coloring will be sucked into the plant right along with the water. Food coloring is non-toxic, so it doesn't poison the plants. If you use enough of it, you may get a little tinting of the leaves and petals of the plant after a while, but the plant still grows pretty much the same.
The leaves and some petals of plants contain many small pores, called stomata. Water evaporates through these pores. As it does so, the plant draws water through its stem, and ultimately from its roots from the soil (or from the water in the vase). This process is called transpiration. Water movement through the plant occurs in xylem, hollow cells stacked end to end to form tubes. In leaves and thin stems, the xylem occurs in vascular bundles that also contain phloem, which transports organic compounds throughout the plant.
Food coloring or dye is very good for outlining the xylem in the plant as it draws the water and dye up the stem. You can see it quite clearly if you cut the stem and look at it in cross-section.
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