Add K1-style draw color block

1. Make a new K1 draw color dropdown block that uses the same style and display/click logic as the image dropdown block.

  ![image](https://cloud.githubusercontent.com/assets/206973/2882051/0af3c778-d48a-11e3-9949-979dc0e9649a.png)

2. Calculate the correct color of the dropdown background based on the semi-transparent backdrop.

  ![image](https://cloud.githubusercontent.com/assets/206973/2882053/16f841ca-d48a-11e3-92cc-248a68b3c756.png)