Are you sure there is no palette? It's probably a separate palette for the glow, with a function dimming it and brightening it. To be honest, if you're going to this level of detail you're probably better off building a titlescreen from scratch, but if you really wanna change it: Open the palette viewer in VBA and tick the Automatic Update box, and watch the yellow palette until it reaches its brightest. Then untick the update button to freeze the box and search for that really bright palette in the ROM.