@ your ground modification :
two colours only seems a bit crude to me, esp. since ground is also walls here and there. I'm not 100% convinced with that "ground should not disctract the eye" approach. I've been playing Sonic II where ground looks like a tetris game ... i've been playing Rayman where ground is a boom of cheery colours, and it never distracted me from the actual gameplay.
And i've been playing those sharewares and freewares where ground was made either of two colours or a single, repeated, tile and been distracted by this "unnatural" look. Imho, a good ground tileset should provide low contrast, but sufficient details so that it doesn't attract the glaze by being "a different area".
Maybe keeping the three-colours approach but with a little-darker light shade will do the trick.
@ "not how the game will actually look" : i got that we're not going to see the ground with such high angles as you're using for modeling. I don't know how much of the "flat floor" will appear at maximum perspective (i.e. when the ground is in the bottom of the screen), but this will be your "critical case", and i guess you will make sure that we don't have the feeling that we suddenly see something all flat by then.