I found the instructions for this kata a little confusing. I feel it would have been much easier to understand if they said something along the lines of "given a min and max, return a random value within the range". Simple and to the point. I think talking about other numbers being scratched out, etc. makes the kata seem more difficult than it really is.

I believe this kata needs additional test cases to make sure once instantiated a ghost maintains its color. Without this test, it is possible to simply generate a random color on request and still pass.

Is there a name for the Codewars color scheme? Is it (or a close variant) available for vim or sublime text?

I really enjoyed this kata, but for some reason it consistently failed while running tests ("Test didn't pass: Unknown error"), but worked fine when I submitted. Not sure if this issue is limited to me or not.

The first thing I would recommend doing is taking a step back and evaluating you're approach to validating the inputs. Currently you're doing a lot of checks to verify that number is NOT a lot of things, when you could simplify your approach by verifying that number is in fact the type of number you expect it to be (research Ruby's numerical data types to determine which type to check for). That should allow you to clean up some of your logic a bit. As for passing the final test, I would recommend checking what value is being passed in, by logging it to the console somehow. :)