I generally use my 12" for the b&w G3 which has OS 10.2.8. When starting up, the display stays black until the boot panel appears; ie, I don't ever see the screen with the gray Apple logo.Haha, that screenshot looks so tiny on my 23" LCD.(which is set to 1920x1080) Did you actually hook your Mac up to a 12" RGB, or did you simply set the res to 512x384?
Just curious...I didn't think that modern video cards took to running those older fixed sync displays very easily.
My guess is that the low-level video stuff doesn't support the low-resolution, but as soon as OS X has more components loaded, then it can toggle the display back on.