The CSS for the admin UI in 5.3.1 has the following definition which affects help text in a variety of places:
#core-selector #has-no-cores span
This is displayed on a white background, making the text with colour #c0c0c0 next to impossible to read. This fails WCAG accessability guidelines and can be checked using this Contract Checker: http://webaim.org/resources/contrastchecker/
Please adjust the CSS for the admin UI to display text in a more highly contrasted colour. Thanks.