.MouseRow is the Row where you clicked with the mouse,
.MouseCol is the Col where you clicked with the mouse.

I edited my post and added center Alignment to merged cells.

With .FillStyle = flexFillRepeat the cellbackground color change apply to all selected cells, but you have to restore to normal after that with .FillStyle = flexFillSingle, as in the example.

.SelectionMode must be flexSelectionByRow, else its not very easy to align text (it moves the first time).