User-reported unhelpful error message

[codeworld-feedback]

Program: https://code.world/haskell#PfJFVB8hc0GYsY6Bwb9Y3Yg

Message:

program.hs:25:1-18: warning: [-Woverlapping-patterns]
    Pattern match is redundant
    In an equation for ‘colSwap’: colSwap blue = ...