After his baptism, Christ began to call the disciples to follow him. Historically, a young rabbi would call boys younger than twenty and so it is sobering to think that many could have been as young as 13 and that even Peter, who was married at the time, was likely not older than twenty himself. In iconography however, the disciples are usually portrayed much older and of varying ages to more easily demonstrate the age difference Peter and the others. They are generally shown as dressed similarly to Christ in white – a symbol here of how we grow and progress in Christ-like holiness on our spiritual journeys. In Orthodox churches their outer garments are either all coloured in brown, in order to let Christ’s red himation draw our focus, or in an array of colours to describe the variety of personalities among them. While their hair styles are slightly varied, St Andrew’s hair is often shown as particularly rough or messy to reference the fact that he was initially a disciple of St John the Baptist, who himself was known to have a rough appearance because of his lifestyle. 
In the icon of the Lord’s Supper you might notice that Judas’ face is shown in profile and that he is dressed in green. This is the stance and the colour used in iconography for those who, being ‘green with envy’ like Satan, turn away from God’s ways to pursue their own will, as did Judas when he betrayed Jesus for money. 
In this icon Christ's hand is raised in blessing as described in the Matthew's gosepl - 'And as they were eating, Jesus took bread, blessed and broke it, and gave it to the disciples and said, “Take, eat; this is My body.” (Matt 26:26)