Add a new slide
Set Layout 'empty slide' (Leere Folie)
Popup -> Properties ('Folieneigenschaften')
Choose Background ('Hintergrund')
Chosse Color ('Farbe')
Choose a solid color
confirm with OK

Run presentation. A small white border will occur on the right and at the bottom of the display.

Create an oversized image with solid color fill and put it on the slide with some overlap. Now the borders will not be visible anymore.

-> I assume a fill problem while painting the background. 
Like FillRect ( 0, 0, width - 1, height - 1) which in windows will give you a similar behavior, because the right border of the rectangle will not be filled in this case. At least for windows FillRect(0, 0, width, height) is the correct code.