Fix clue color not actually showing

Summary: Found in testing that the clue doesn't actually position correctly or show in blue because I put the logic in editor.less rather than perseus.less. Oops, won't make that mistake again.

Test Plan: Check that it actually works in practice by using make all, going to webapp and making/previewing a question

Reviewers: alex

Reviewed By: alex

CC: alpert

Differential Revision: http://phabricator.khanacademy.org/D7206