Final answer:
The color of light should be in the first column of a data table in this experiment as it is the independent variable impacting plant growth.
Step-by-step explanation:
In an experiment where radish seedlings are grown under different colors of light, when creating a data table, the color of light would typically be in the first column as it represents the independent variable. This is the factor being changed in the experiment to see its effect on the dependent variable, which in this case is the measured height of the plants. By placing the colors of light in the first column, it allows for an organized and clear comparison of how each color affects the plant growth over the eight-week period.