Please look at the three portraits above. Well, that's the master of the house in the middle and his wife to the left; they are the Babah and Nyonya of the house. Who is the person in the right then? Well, it could be his mistress, who was of Indonesian origin. Back then, it was a common practice for a husband to have more than just a single wife. Of course, that practice doesn't occur in the current Indonesian society anymore, not out in the open, at least.
There is popular novel by Remy Silado, titled "Cabaukan" about this particular aspect in Jakarta or Indonesia in the 1930's or so. Based on that novel, a movie with the same title was subsequently produced. If you want to know more about it, please google the title and rent the movie/novel. I watched the movie several times, not because it was really great but because I could connect to the circumstances some 80 years ago and I could hear funny expressions from the past, some of which I didn't remember they even existed until I heard them again in the dialogue of the movie.