John wants to know if the color of the syrup (food) in a hummingbird feeder influences whether hummingbirds feed at the feeder. john set up his experiment this way:

john selects 6 identical hummingbird feeders. he prepares a sugar water solution for the syrup (food). he divides the syrup into 6 equal portions. he adds different colors (food dye) to 5 of the portions of syrup (food). he adds the syrup (food) to each of the 6 feeders. the feeders placed equal distance apart on a long fence in the middle of a field. john leaves the area so the birds are not disturbed by human presence. the feeders are collected after 6 hours.

what is the feeder clear syrup a independent variable ,dependent variable, constant or control?