User-reported unhelpful error message

[codeworld-feedback]

trafficstars

Program: https://code.world/haskell#PRo2oDb2J8XRxvt4ZObDM6w

Message:

program.hs:32:15-21: error: Outdated use of gray as a function.
    Remove the function argument for a medium shade of gray.
    For a different shade of gray, use light, dark, or HSL.