Thanks that pointed me in the right direction!
However – I didn’t have the control that is needed to make the UI usable! There is a control in Text Editors > Annotations that controls the Occurrence highlight color. There I can make the highlight bright RED, this is not very readable in the text of a Java file – but it does make the Occurrence indicator on the vertical “overview” bar (beside the scroll bar) visible. But only in the poor side effect that the indicator has a RED border but the inside of the rectangle is still the color of the overview bar, i.e. the rectangle fill is the same color/shade as the background – but now I’ve got a Red rectangle. Better than no visible rectangle at all. However making the highlight color such a bold shade is not desirable!
Note: on the Mac – there is no Windows menu – it is called “MyEclipse” and there are two menu items with that name, both have a item “Preferences” but they appear to do different things. The MyEclipse (the Application name – the left most MyEclipse) appears to control more of what the Windows > Preferences does on the PC. The other “MyEclipse” (the right most item) appears to control project preferences. Quite confusing if you ask me.
David