A wiring-like library for the small HW-oriented linux systems seems like a good idea, but I'm not quite sure how it will be "simpler" than a rasberry Pi. You pretty much still need to do all that "unix system administration" stuff 
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No, of course all linux software won't run on it. "all linux software" won't go from Ubuntu to DSL without some care. Since the board is an ARM board, presumably its linux is somewhat different from x86 linux systems, and you'll at least need to recompile. Which can be hell, as I know just from trying to get x86 linux software to compile on my x86 Mac.
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Maybe. It's got more and different IO than a RPi, a different core cpu, and presumably a different video setup.
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In quantity, board color is probably an insignificant modifier to price. Some vendors seem to have settled on particular color schemes as their personal standard. Blue for Arduino, Red for Sparkfun, Purple for OSHPark, etc. Anything but the old "industry standard" of "green." A color that hides the traces can make the silkscreen labels more visible, which is good. But of course it hides the traces, which is bad.
All these small unix boards are pretty neat. It sure beats converting some consumer device (chumby) that stops being sold
I do wish that I had more confidence that which ever board I pick will actually be successful enough to continue to be sold, rather than becoming one of the "well, we tried that, but RPi was too tough a competitor" might-have-beens.