Damn, those pics make me want to pull apart my gakken and paint it (probably ruining it in the process, haha)
I bought that Imai kit - painted and built it. It is a really nice kit in proportions, but it is pretty fragile (well, it is a kit, not a toy). I have left mine in armor mode. I only transformed it once.
PS - you would definitely have to paint it. Kits that are molded in colour rarely make the grade without painting. maybe except MG kits.