In Test Match cricket, what colour have the "sightscreens" (the large screens behind the bowler, designed to aid the batsman's view of the ball) always been?

Sightscreens in Test Match cricket have traditionally been white because they provide the best contrast for the red ball used in Test cricket. White screens allow batsmen to clearly see the red ball against the background, improving visibility and timing. Black or green screens would not provide sufficient contrast with a red ball.