It has been a while since this thread was bumped and I didn't feel like making my own, new thread, so here goes.
I first wrote about this idea in
markee's reply to Compatibility with Messenger 2009 Beta but it wasn't acknowledged. I seriously think that it can't be too much effort for script developers to now have control over the colour of toasts and adding their own images to where the DP normally sits. It would be very nice to have this ability so that toasts were easier to recognise if they were coming from a particular script. Admittedly, I would love the ability to use my own plus window (even if we had to use the exact same dimensions), but I guess that would be asking a bit much when there are many other more valid features to be added first that are all scattered throughout this thread.