Not sure Oda has it set up this way, but more closely related to the Chinese zodiac theme: Dog, Bird, Monkey, Tiger, Bull, Pig, Rabbit, Snake, Dragon, Rat, Goat, Horse.
Akainu: (Red) Dog
Aokiji: (Blue) Pheasant/Bird
Kizaru: (Yellow) Monkey
Fujitora: (Purple) Tiger
Ryokugyu: (Green) Bull
Chaton: (Brown) Pig
Momousagi: (Pink) Rabbit
My guess is there are 5 more VA's (Horse, Dragon, Rat, Goat, Snake) that fill in the "Admiral" recruitment/conscription that Akainu imposed to be his "New Marine HQ", but they weren't qualified to be Admirals, like Chaton/Momousagi.
Yes, one of them should be Orange. I assume 2 others will be Black and White. Not sure what the last 2 would be. The reason I say that Orange probably doesn't "fit" Oda's motif here is because Chaton is "Brown" Pig and Brown is just a mix of the 3 primary colors, and yet is only a VA.