Why does Colin remove the curtain from his mother's picture? What does this tell you about Colin?

From the text:

"I know what you want me to tell you," said Colin, after she had stared a few minutes. "I always know when you want me to tell you something. You are wondering why the curtain is drawn back. I am going to keep it like that."

"Why?" asked Mary.

"Because it doesn't make me angry any more to see her laughing. I wakened when it was bright moonlight two nights ago and felt as if the Magic was filling the room and making everything so splendid that I couldn't lie still. I got up and looked out of the window. The room was quite light and there was a patch of moonlight on the curtain and somehow that made me go and pull the cord. She looked right down at me as if she were laughing because she was glad I was standing there. It made me like to look at her. I want to see her laughing like that all the time. I think she must have been a sort of Magic person perhaps."