if you have your order the other way, with red, yellow, green then you can do index - 1, and you won't hit your error - because 0 - 1 is -1 and that gives you the last item in the list - which is green, and the correct value.

Check your data types throughout.

You're able to debug by adding print() statements, so you could print out the inputs, and then check teh inputs for the one that isn't passing and work out why.

You can not 'sort' an integer, it's an operation that would make no sense to python.
So we need to change it to a datatype that python can sort - strings.

1. Change the number to a set of strings.
2. Sort the set of strings into reverse order.
3. Join those set of strings into a single string.
4. Change it back to a number.