Anyone knows when BRB changes color ?

[PoiSoNouS]

I have some BRB, and I noticed some color changement. I don't know why it changes color and wonder if anyone could explain to me. Does it changes with humidity or heat or how he feels?
He changes between grey and white on the sides:

<img src="http://www.deepvoid.net/snake/images/boa/pages/images/boa4.jpg"> <img src="http://www.deepvoid.net/snake/Juv_11.jpg">

Thanks

Mary

[Linds]

Perfectly normal. They get white-sided in the evening usually, and darken up during the daytime. IMO their overall colour improves during the night as well.

[backdraft1320]

OOH OOH CAN I HAVE HIM LOL
VERY NICE

[Jeff_Favelle]

Night time man. The sides turn grey/white around an hour or so before dark. I found that the more contrasting the color change, usually accompanied the prettier snakes. But there's always exceptions.

[PoiSoNouS]

Thank you all :)