Mysterious friend

Sebastian started talking about 'Ranke Kalut' about a month ago. We still do not know exactly who it is. According to Sebastian he is black, green and white. However, he can change colour. He does not have a mouth, ears, nose and he can fly. We have tried, in every way, to figure out who it might be (from a movie, from a book etc.), but it seems as though this Ranke Kalut is an imaginary friend. Then last week Sebastian made a drawing of him:

Hmmmm... this time he was red and brown it seems. We hope, obviously, one day to be able to meet this 'best of friends' - until then we remain rather confused!