They are dressed in lavish clothing with red bedding and a dog to show their status and wealth. Even the way their are positioned is symbolic. She stands closer to the bed and deeper into the room showing her as caretaker of the house and representing her womanly role even more clearly. The green of her dress is hope and rebirth (think spring) while her head covering is white (purity) and the bed clothes are red (sex). Absolutely everything in this painting is there for a reason! Even There is a carved figure of Saint Margaret, patron saint of pregnancy and childbirth, as a finial on the bedpost,. Saint Margaret was invoked to assist women in labor and to cure infertility
Finally, please note that there is only one candle lit. This comes from an old Flemish wedding tradition to evoke the eye of God.
Other cool facts here: Notice the small mirror in the background? Van Eyck actually painted himself into the painting in that mirror as a reflection! Some think this is another sign of the eye of God. Also, directly over this is the artist's signature, in a gorgeously central spot yet almost camouflaged.
Finally, this was actually painted with tempera on wood!
There is even more symbolism in this piece that I am not listing and that I do not fully understand so I greatly encourage you to keep reading about and other of Van Eyck's works! Every time I run across this painting I discover a whole new layer of meaning!