64 colors ?
Every Amiga (except few very early A1000s) do support 6Bit modes.
OCS/ECS only EHB and HAM,and AGA real 6Bit (well and 7Bit and 8Bit too).
The A600 didn't have anthing the A500+ didn't have in that field, the only difference
where the switch to SMD (bad), the PCMCIA-port and onboard IDE.