Xcode15 quicklook renders this as a one solid red color square on a P3 display, while the NSImageView displays it as a 2 different shades of red on a P3 display.
let size = CGSize(width: 250, height: 250)
let image = NSImage(size: size, flipped: false) { drawRect -> Bool in
let rects = drawRect.divided(atDistance: drawRect.size.width/2, from: .minXEdge)
NSColor(displayP3Red: 1.0, green: 0.0, blue: 0.0, alpha: 1.0).set ( )
NSBezierPath(rect: rects.slice).fill()
NSColor(red: 1.0, green: 0.0, blue: 0.0, alpha: 1.0).set()
NSBezierPath(rect: rects.remainder).fill()
return true
}
imageView.image = image