Yesterday description of exercise talked about colors function. Today there is nothing like that.
There are two exercises that involve resistor colors: Resistor Color and Resistor Color Duo. Only the first has a colors function. Are you mixing them up?
I confirm that the exact linked solution is a valid solution for Resistor Color Duo. There should be no error when running the tests for that exercise with that exact solution. But I get exactly the error you mention if I make exactly this change: