Pie chart colors can't be changed

[madalincm]

Steps to Reproduce:

1. Open a query that has a pie chart visualization: https://pipeline-sql.stage.mozaws.net/queries/336/source#395
2. Click on edit visualization button go to the colors tab and try to change any color

Expected results:

The colors can be changed

Actual results:

The colors can't be changed

Notes/Issues:

Build identifier: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:58.0) Gecko/20100101 Firefox/58.0
Verified in FF58(Win7). Issue can be reproduced in STMO-stage only after the ui changes were applied.

[madalincm]

Verified as fixed in FF59(Win7) in stmo-stage
Postfix screencast:

Marking bug as verified fixed.