When viewing feed entries as websites while using a dark color scheme, and if the website did not define some background color for html or body tags, you may end up trying to read black text on dark background, which is difficult to say the least.
It would be great to be able to set an (optional) default background and text colors for displaying websites, overriding the application background color set in the KDE color scheme. Similar to the preferences / content / colors options in Firefox, which provide a very basic CSS reset that in turn is overriden by the website's css itself.
As an extra (similar to the mentioned Firefox dialog) you could also chose default normal and visited link color, and also apply these choices when displaying the feed content instead of the website itself.

You may wish to make this request in the Brainstorm or on Bugzilla.