Dark Green with Orange Koala is a fanmade Sing-a-ma-jig Duet. The big one is dark green, has blue hair, black circle eyes, a red nose, a purple mouth, the same hand pose as the big one from the Orange duet, and the same feet as the Ghost. The little one is orange, has the same ears, hands and feet as the little one from the Gold duet, circle eyes which are colored the same way as the eyes of the big one from the Orange duet, a green nose and a purple mouth. They sing "It's Raining, It's Pouring".
Here is what their voices sound like.
Big one: Mint Green
Little one: Little one from the Sea Green duet (whilst singing, harmonizing and chattering in the same voice as the Skeleton)
Here's how they sign on, enter song mode and sign off.
Sign On: Both: "Hello!" (Big one first)
Entry of Song Mode: Both: "Song!" (at the same time)
Sign Off: Both: "Bye Bye!" (at the same time)