jquery 1.12.4 console errors on admin pages

Running WP 5.1.1, which incorporates the stock jquery 1.12.4.

In the admin sections, I get the warning below, and some functions are not working correctly.

“The specified value “!” does not conform to the required format. The format is “#rrggbb” where rr, gg, bb are two-digit hexadecimal numbers.”
http://www.domain.com/wp-includes/js/jquery/jquery.js

Is there a fix for this error, and where to get it?

Thanks,