For the time being you can add a highlight only in the timeline area (the one with the bars and connections between them) using the TimeLineVisualizationBehavior
feature of the GanttView control. We are planning to add such feature for the Grid area as well, but its development is not scheduled yet.
Currently the only way to change the font color for a specific row is by using custom CellTemplates in which the TextBlock's Foreground is bound to a specific property of the Task through a converter. I must warn you that this approach costs performance.
Hope this helps.
All the best,
the Telerik team