Rainbow fringing around every edge, far more colourful than any real lens would produce.
It starts like ordinary chromatic aberration, pulling the colour channels apart by an amount that grows with distance from the centre. But instead of showing you that, it measures how far apart they ended up and throws the colours away, keeping only a single number for how strong the fringing is at each point.
The rainbow is then invented from scratch. That one number is stretched across the entire colour wheel and given full saturation, so a narrow range of edge strengths becomes every hue there is. This is false colour, the same technique that paints heat maps and weather radar, applied to edge strength.
The original picture is drained of its own colour and added back underneath, so you get a grey image wearing a rainbow outline. passthru sets how much of it shows.