Color detectors can be useful in a number of ways that go beyond capturing hex codes:
CHEMISTRY: Convert hex codes to HSV to derive the Lambert-Beer law in chemistry.
Try this lab from Science on Stage Europe: "How Deep Is Your Blue? - Coloured Chemistry with Smartphones"
PHYSICS: Observe colored flowers or candies under monochromatic light, and use the detector to objectively record the colors of the objects as they appear under different lights.
Note: Students who observe multicolored candies under red light, for example, tend to refer to the red candies as "white" in contrast to the other candies that appear black.
BIOLOGY: Observe the changes in a fall foliage by observing a standard leave across a period of time.