(resubmitting this as a problem, since resetting preferences to default did not work the next time I opened Photoshop)
I am running Photoshop CC 2017, with the latest update.
Open a New document - US Paper, default settings. Or open any other type of document. Verify Color mode: RGB.
No matter what I do, the color picker palette will NOT appear, either in this new document, or in old documents where the palette formerly worked just fine. Using the "X" shortcut key, I can switch colors from black to white, but the foreground/background color icon does not switch in the toolbox. I've restarted Photoshop multiple times whilst holding down control-alt to try to reset Preferences to default. No joy. Gone thru all my preferences... nada.
I was finally, after many attempts at holding down control-alt and control-shift-alt, able to force the Preferences back to default. Voila - the color picker palette reappeared. BUT: the next day... and the day after that... the same problem happens all over again. No palette.