Answer:
the different colors of light
Explanation:
In an experiment, the independent variable is the variable that the experimenter manipulates or changes in order to effect a response in the dependent variable.
In this experiment where Sam is trying to find out if fish are attracted to different colors of light, the independent variable is the DIFFERENT COLORS OF LIGHT because it is what the experimenter changes in order to bring about a response in the dependent variable (number of fishes attracted to the light).