Did you notice how Excel uses animation to move the selection marquee? That effect makes it easier for the eye to follow the selection.
You can add a similar effect to the FlexGrid by adding a transition to the style of the marquee and cells. See the effect by selecting a cell or a range with the mouse or keyboard.
In addition to the marquee, you can animate the grid cells as well. This effect shows when you resize, drag, or sort the columns.