The cel appears to be from the second chapter, Curse of the Overfiend. The scene is that where a majin is running through a subway and is basically annihilated by Amano, after which there is a close up shot of our favourite Jujin.

Now my cel is in shades of blue, but that's not the colour of Amano in the footage. I trust it it a genuine cel as the image is spot on aside from the colour and it was purchased from Mandarake's Nakano Store. So, what's going on?
I was thinking that perhaps a coloured transparent sheet was placed over the cel (like you would a light in theatre) to demonstrate some kind of emotion, but I don't know anything about that aspect of production.
Does anyone know why it would be a different colour?