GridViewRow and GridViewCell SelectedBackground properties will be part of our next LIB version 2018.2.820. These new properties will also be included in the next official version – R3 2018, scheduled for the mid of September.
Jus For applying back color and fore color of gridview selected row 500 lines of code is simply madness , it should be as simple as setting alternate back color of gridview.
Alternatively, you can have the Background property of DataGridRow (or whatever that's called) (with a RowStyle) to have an effect when IsSelected is true.