Blue stripes are often created when a crevice in the ice sheet fills up with meltwater and freezes so quickly that no bubbles form.
When an iceberg falls into the sea, a layer of salty seawater can freeze to the underside. If this is rich in algae, it can form a green stripe.
Brown, black and yellow lines are caused by sediment, picked up when the ice sheet grinds downhill towards the sea.
Link (with more pictures) -via Geek Like Me
(image credit: Oyvind Tangen)