Check for a bad trace near the 68000 cpu and/or maybe Fat Agnus has a problem (try reseating it but do use a proper PLCC tool). As for the battery, even though you removed it, that acid could have leaked before and unless neutralized will continue to eat at a trace. I have an A2000 that had corroded the inner pins of the 68000 socket just from the gases coming out of the battery, even though the m/b near the battery showed hardly any corrosion. The only fix is to desolder the socket and replace with a new one.
Yellow is a hardware exception error so it could also have something to do with the Buster subsystem (a classic example of this is when you try to boot an A3000 desktop without the daughterboard installed). Red usually is a ROM problem. Green is a chipram problem and Blue signifies custom chip problem(s). Black/dark grey screen means cpu error (if you see a yellow screen at least the cpu is initially working). Light Grey screen means it almost will boot but is getting hung up on the software side just before boot (maybe fastram problem, Bridgette on A4000, Budgie on A1200 or even a bad CIA could be responsible).
