Attached is my BMW logo background (480x234). This is the actual BMP file I used to replace my CPYCUSTOM and CPYDEFAULT files.
The logo itself is a bit foreshortened top-to-bottom so that on my screen it is a circle and not an elongated vertical ellipse.
The black is RBG 10-10-10. Whenever I used 0-0-0 or anything less than 10-10-10 (such as 2-2-2) the screen would look great for about half the boot up, then all the black would turn a crappy grey. I played with the backgrounds forever to get this one right on my Z3
for kicks I also attached my phone ringer icon that I changed to match my Blackjack