No please why did you make this, can you even implement this into the game???
The reality of knowing that this thing probably won't even be in game wrecks me.
UI windows in FL are 3d meshes with pre-sorted depth, so technically they can be replaced entirely and not just recolored, but they'll always exhibit anti-aliasing unless you make them for the very specific resolution and forcibly turn off texture filtering for the entire game, so single-pixel borders aren't really practical to do, scaling will kill them anyway. Aside from that another problem for positioning would lie with text rendering, which in FL is done as a GDI overlay.