Can I define my own colours for highlighting?
Yes. You find the dialog Colors and Syntax Highlighting under Options | Highlighting. In the first tabbed pane Selections and Colors choose the 5th button Customize Basic Colors, which opens a new dialog, where you can change any of the 16 colours. Note that highlighting can look weird if you choose completely different colours. You can always return to the default colours. In Version 5.3 of WinEdt go to Options | Preferences | Colors and open the context popup menu (Rightclick on Colors). Then choose Change Colors to redefine the colours.