I have the same problem, on one page. After upgrading to 3.8.1, the text in the editor is white (#FFF) on white background, as html code on the text tab. The visual tab will not work on this page.
As a temporary work around I updated line 1 in the styles sheet: wp-includes/css/editor.min.css
change…
.js .tmce-active .wp-editor-area{color:#FFF}
to…
.js .tmce-active .wp-editor-area{color:#333}
I’ll continue to poke around to see what I can find.