Just a thought, but is it just a little bit of ghosting, rather than an extra colour?
In Ristar, in the first level, there's a colour in the background that shows up only when I'm moving, and disappears when I'm standing still.
It's not like that on real hardware.
P.S. In Sonic CD, the music does restart again later, it just takes a really long time (I'm not sure if it was like that originally).
There is generally only one track per level (except when you gain a power-up), and on real hardware, it repeats immediately.
I think just the access times on the cd take ages to get to the next track. It seems there are quite a few different tracks used on one level.
Just making a note of it.