from entrpntr

nopal - no inputs on bootrom

pal - standard selection of a palette (press & release) (with buffered save, can buffer palette with a or b and release before ~86 frames)

nopal(ab) - press or hold one of A/B/START/SELECT (which doesn't select a palette)

pal(hold) - select a palette, and hold the inputs until the bootrom completes

pal(ab) - buffer a dpad input during the hard reset, add A or B between when the 'E' and 'B' in 'GAME BOY' appear, and hold both inputs through the end of the bootrom.

GBA        GBC
           pal
pal        pal(rel)
pal(rel)   nopal
nopal      pal(hold)
pal(hold)  pal(ab)
pal(ab)    nopal(ab)
nopal(ab)