My guess would be that it's an attempt at making it very clear whose blog you're on, to disambiguate.

http://svbtle.com/ now has colours for each member blogger, and it looks like they all have their own left sidebar slideout thing. Additionally, their pulsing icons in the top left have an additional colour hint to them.

Edit: I think it's a little too intrusive and clashes with the overall feel of the rest of it, but that's just me!

Hrm, I thought it was actually kind of nice. Soft, non-obtrusive and gave a lovely "alive" feel an otherwise cold page. In fact, does anyone know of any tutorials on how to do this?