It is under Preferences > General > Editors > Text Editors. There is a checkbox labeled “Show whitespace characters”. If you uncheck this the editor switches back to normal.
If you click on the “whitespace characters” link in this line you will get a popup window, in which you can define which characters eclipse is supposed to consider as whitespace characters.
In this popup window you also get the option to define the transparency in which each whitespace character is displayed in the editor, which you can use to (indirectly) change their foreground colour. I’m just mentioning it here, because it took me about half an hour to find this setting! 😉