I just installed the latest BuildBot from the Blender "Bleeding Edge" downloads. I checked, the color picker is working fine. I enabled Node Wrangler, still fine, enabled PBR Materials, still fine. Tired Asset Manager, (which the developer has stated is not yet 2.78 compliant) and the CMD window was coughing up hairballs, for the moment. Seems like your team has snuffed out this one. Congratulations. Best to you on the 2.78 release.
Dec 19 2018
Sep 6 2016
I checked, and I have never changed the defaults. I tried them all and they all seem to work, when just going over to the 'nearby' color choices in the User Preference window, so those do not seem to be a problem. I will look forward to the next RC and see if Node Wrangler acts better. I know that Asset Manager hasn't stated 2.78 compliance yet, and I do not know about PBR Materrials, as both of these threw up 'complaints' in the CMD window. Thank you again for your response and your team fine development work.
I tried the Factory Default, color wheel worked fine, thank you. Node Wrangler, downloaded the latest from their site, but the problem was still present. Turned off Asset Management and PBR Materials as I saw some error warnings in the CMD Window, and turned off Node Wrangler. Color wheel works fine. So "one" of them appears to be contributing. Thank you again.