Greetings Patrick,
I do not think there are options to change this element. SAP GUI allows to change the background colour quite freely, but not the text elements' colour.
The only workaround I can think of is to set the background in SAP GUI to a colour that has a high contrast to the blue of the highlighted elements, such as sand dune yellow or something along those lines. You can create your own Background colours theme in SAP GUI options for "Visualization", option "Color Settings".