Mines is gab blue its a good colour, though I have two tone leather (tan in the middle of seats and door cars and black elsewhere) in fact the interiors in my past three cars have been two tone once you have had that you won't want another sombre black interior, check a few out it really brightens up the inside makes it a pleasurable place to be not that it isn;t normally its just nicer IMO is natural momo tan colour like I have? if so then yes its cool I am a bit clueless when it comes to the specs and stuff
I had a Gab Blue 156, with Natural Leather, for a short while, and IMO it didn't gel, much prefer my current colour choice Brilliant Blue, Grey Leather.
I know these aren't 147 options, but I think Cas Blue, with a dark Grey would be better. Natural looks good with Red, or Black IMO.
Alfa Rosso with black leather (only time I would ever take black leather seats in any car - or red paint for that matter).
Metal black with red leather seats (same thing, but the other way around, and again, I wouldn't want red leather seats on any other car but an Alfa or a hideously expensive sports car).
Sail Blue with beige cloth interior... which is what I have because I thought leather was a tad expensive . Actually, mine is velour, which I think looks less nice then cloth, but I'm a sucker for the way it feels.
Summary: if you can afford leather on your Alfa, go for the sports car look all the way, if not, blue is a great colour and the beige colour really livens up the car with the two-tone interior (with black and grey cloth it looks a bit like a poor man's Alfa without the leather, but the beige tone makes it look a little more sophisticated).
I've got black met and red leather, took some time to get used to it, but I must admit it looks brill, have seen no other combination to match it. I've had cosmos blue and black sports (not bad) and sterling and blue, very light and airy.