What RGB color values do you have defined for your fourground and background marking region
You can find this out by going to the Document Type, Color panel, selecting the Marked Area option, then double clicking on the color square.
In the old Zeus when you select in column mode there is no indication of an active selection. With this version Zeus will simulate a column selection by crearting a color that is close (but not identical) to the current marking colors.
What might be happening is that because of you current marking colors, this simulated color might be somehow overflowing the RGB ranages
You could also try altering your current marking color.