image source: closer to van eyck
The sky is blue and so its colour symbolises heaven and holiness. In the Just Judges panel there are five figures that bear the colour blue. Two riders wear blue coats and two others are given blue hats. The fifth figure, the rider at the corner point of the group, wears a hat with a band of blue circles.
Blue is also the colour associated with the Virgin Mary.
Seemingly Jan van Eyck has colour-coded the four riders to associate them with some aspect of holiness.
The bearded figure placed behind Jan’s brother Hubert in the forefront has four identities. All of them are associated with “holiness”. At this stage I’ll mention just one: St Bavo, patron saint of Ghent and the Cathedral Basilica where the painting is housed.
St Bavo was a soldier said to have led a disorderly early life. After hearing a sermon by St Amand preaching against a life based on riches, he became a Christian and later a monk.