Could be colored or touched up. Not my area. I see that all three postcards have the same striking shaded colored skyline, which suggests a touch-up. There are plenty of colored postcards on my page:
http://www.antiquegamblingchips.com/AguaaaaaaaTest.htm

If you are interested in the place, you could buy the soft-cover, inexpensive, recently written book about the place -- Paul J. Vanderwood's "Satan's Playground : Mobsters and Movie Stars at America's Greatest Gaming Resort". Only $8 delivered.
http://www.ebay.com/itm/Satans-Playground-Mobsters-and-Movie-Stars-at-Americas-Greatest-Gaming-/371036194089?pt=US_Texbook_Education&hash=item56637b0529

Paul corresponded with me, helped a lot, died recently. RIP.

Robert