I'm not too sure as I don't actually own them. I am shopping for one for the near future (Final Fantasy was released on them)
I think it went
Wonderswan = Gameboy
Wonderswan Color = Gameboy color
SwanCrystal = Gameboy Advanced
I'm not certain though because sources claim that both the Wanderswan color and the SwanCrystal rivaled the Gameboy Advanced and I don't think they had seperate game releases. (like the GB color and Advanced did)
But yes, Wonderswan was black and white games whereas Wonderswan color had different colored games (but was backwards compatible)
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Edit: after research, the swancrystal was just an upgraded wonderswan color. It did not have unique releases.
I will be adding games to both categories tonight to give them a little start (packing the computer tonight for the move though)