I think you might be right. Seems rather to common/obvious an element of source code for them to forget about though!?
It might be worth while raising a bug: http://cfbugs.adobe.com/bugreport/flexbugui/cfbugtracker/main.html.
If you report the number back here, I'll vote for it.
I found a work-around by setting Preferences->General->Editors->Text Editors->forground color.
Seems it should be more direct than that - most languages in Aptana have an "IDENTIFIER" color set.