I think octal literals are Very Dangerous Things™, and I'd like them to be glaringly obvious whenever I read source codes.
There must be a way to do this in Eclipse, right?
So it looks like standard Eclipse cannot be configured to do this? A custom colorer is required?
No, currently you can only configure a color for all Numbers in Preferences > Java > Editor > Syntax Coloring. May I suggest creating an enhancement request at the Eclipse Bugzilla at http://bugs.eclipse.org/ (correct project is imho JDT / text)?