I can't replicate exactly what you are doing, if I use something like this
Private Sub Command1_Click()
fg.Cell(flexcpBackColor, 2, 2) = vbGreen
'fg.BackColorSel = vbGreen
The the cell(2,2) would have a green background and on selection it would be overridden by the default selection color. However if you have defined somewhere the fg.BackColorSel then the HIGHLIGHT color would be overridden by the BackColorSel property
Let me know what you are trying to do ,may be some sample or the steps exactly would be helpful in narrowing it down
Also if you can check the scenario with latest build, if you ain't using that.