Hi
There’s this “break” when the user logs in currently, with the “Ubuntu MATE” being abruptly moved from bottom to center screen.
My two cents: it’s not pretty.
For a few install now I’ve done the following:
The effect is beautiful, with the desktop lighting up with colors once the user logs in.
What do you guys think?
Yes, nice idea. I have done this for a couple of weeks.
But at the moment i am switching my desktop background almost every week. 
Funny you should mention this today when just last night I installed 16.04.1 on Grandson’s laptop and noticed this exact same thing. It looked strange and made me wonder if there was a graphics problem. I guess I never see it on my systems using my own backgrounds.
Only sometimes, I get a NVIDIA logo on the main screen for a split second before the greeter takes over the screen. Annoys me to no end, even more so because it shows up split in half on the main screen on account of my dual-monitor setup.
Also for some reason, I never got the nice load image during boot that I saw the other day on another computer. My installation boots up with a black screen until the greeter shows up.
Edit: I love your idea. I already use both with the same background for a long while. But I think it will look great if I adopt your idea. It's an almost B&W background with a sepia(?) tone. I can imagine the nice effect it will give if I make a pure greyscale image for the greeter and lighten it up a bit...
Images can be symbolically linked. Knowing this, you can make any image on your system the same thing across everything, without needing to redefine your images everywhere.
This does have a limit; You’re forced to use ln every single time you want to change the desktop background, or you’re forced to come up wit your own bash script to cycle through images by first selecting an image at random, then using that image in a small program which would replace the symbolic link, and overwrite the previous one if you wanted random images everywhere which matched.
I do this too, and I am surprised it is not default.
I don’t want this. I set a different background for the greeter and another for the actual desktop work. It’s nice to have different images that show you that you are on different spaces.
The system itself broads some wallpapers with and without the logo and in different places and colors. It may be time to choose one of them (or the one you create) for next release.
ps: I get the nVidia logo sometimes too but it is not a logo, it is a HUGE logo, it takes the whole screen.
