Sable -
Sable is a very interesting coat color; though, technically it is not a color. Sable refers to dark tipped hairs. Most often, the colors on the coat will be in the brown - grey color range. The darker tipping will be black or very dark brown (chocolate sable). If you were to push back the hairs, you'd often see a white/cream/light tan color towards the roots.
When you look at the colors of a Maltipoo, you look to the colors of the Poodle, since Maltese dogs are only found in white and sometimes cream. Sable is not an accepted color of Poodles, but does exist. It is very rare. And therefore, it is very rare with the Maltipoo.
While it does not always occur, the dark tipping of sable coats may fade off as the Maltipoo matures. This is because as the coat is trimmed, the tipping is trimmed off. With some, new hairs will be dark tipped, but with others, newer hairs may hold the lighter, inner color.
In essence, just like with other coat colors, a young sable Maltipoo may look quite different as an adult.