Resolves T3360 - notDefaultColor() is causing an error

Summary: The logic I was using for allowing wrapping a single callback into an array was broken

Test Plan:
- Paste the code from the task into the tests for a challenge
- Complete the challenge
- Verify that it fails if you use red

Reviewers: john, pamela

Reviewed By: john

Subscribers: #cs

Maniphest Tasks: T3360

Differential Revision: http://phabricator.khanacademy.org/D14656