green PCB is latest, they never made a black pcb as far as i know... (I occassionally keep in touch with the AK team so I'm pretty sure).
i am in touch with the acekard team, all of my 2.1 came directly from them.
the 2.1 comes in a dark green pcb, light green pcb, black pcb, and blue pcb. black and light green being the more recent design and the one that ships more often. the 2i came in green and black. the blue was mentioned but i can't confirm that it ever shipped.
i'm using the black on in my nds right now to play warioware.
http://wiki.gbatemp.net/wiki/index.php?title=AKAIO#F.A.Q.
CODEWhat are the differences between the various builds of the Acekard 2s?
The AK2 suffered from a manufacturers soldering error. This problem caused the later batches of the Green PCB AK2 to experience a FAT issue. The cards would stop working some time between 2 weeks and 8 months, depending on usage. The AK2s were then pulled and fixed, relabeled, and released as the first batch of AK2.1s. These fixed, light Green PCB Acekards, have a small chip under the sticker. They are essentially the AK2 repaired, which means the internals are the same. The kits were later redesigned and re-released as the AK2.1 Black PCB. The Black PCB contains a new controller chip and features a permanent redesign of the PCB which insures that FAT error will not happen again. The Black PCB AK2.1 was offered in a new package design, a box, and sold with or without the AK microSD reader. This version of the Acekard 2.1 was also issued as a darker Forest Green PCB. The kit then went back into development and was released a 3rd time with a metallic Blue PCB. The Blue PCB features a new shell. Acekard took out the spring loaded microSD slot and the shell clips in favor of glue.
The FAT error AK2s are no longer in circulation. You can not purchase one and you can not ask Team Acekard for one. The old shell AK2.1s are slowly being phased out as parts and supplies are used up in favor of the new shell and Blue PCB. In the end all versions will work and do what you expect. Do not panic if you receive a Green PCB over a Blue PCB.
The 12/01/09 Acekard 2.1 builds appear to have the same hardware as previous versions but suffer from firmware compatibility issues. It is recommended that you do not purchase one of these batches.