Bring back colorpicker updating

Summary:
Looks like I left this code out of the blockly refactor. :-/
This change just brings back the code.
TODO: Test Hotnumber up the wazoo

Test Plan:
- Create two fill commands in a program, make them different colors
- When you click on each, you see the appropriate color

Reviewers: brian

Reviewed By: brian

Subscribers: #cs

Differential Revision: http://phabricator.khanacademy.org/D12675