Rather than Flash lite 2.x, you can not modifications its _focusrect property. By default _focusrect be yellow box around.
You can toggle _focusrect by using
_focusrect = false;
Using the SetFocusRectColor command within your Flash Lite 2.x and 3 applications is easy, as there is a custom fscommand2.
fscommand2("SetFocusRectColor", 0, 0, 0);
Selection.setFocus(any_mc);
You need to set the color to replace 0,0,0.