ABANDONED. A boy with an alien in his head (not Chocky)

[Emily]

I read this book in the early or mid-90s, which leads me to believe that it is likely a young adult book. The story is told from the perspective of an older sister and is about her younger brother who, I believe, comes to have an alien presence in his head. At some point, he paints his room black, possibly with stars, and he spends most of his time in his room. For years, I thought this was Chocky, but I recently read Chocky and it's definitely not the book I was thinking of!

[Lobstergirl, au gratin]

Emily, are you still looking for this book?

[Emily]

Yes, I am! Sorry, been overseas and not very diligent in checking my email. Any leads?

[Tab]

Del-Del somewhat fits. I think it's told from the sister's perspective.

[Ann aka Iftcan]

How positive are you that it was told from a sister's pov? There is a series of 2 books about a boy with an alien symbiote. Needle The second book has a younger sibling Through the Eye of a Needle

[Lobstergirl, au gratin]

Still looking?

[Lobstergirl, au gratin]

No response in 2+ years. Moving to Abandoned.