I personally feel that an Artisocrats style build should focus on two colors. Three makes the mana clunky and the deck less focused. The best second color is probably either red or white. The basic shell of both are the same with just a few minor differences due to the splash color. So, here is what I would look to do in either case:
Obviously the numbers would be tweaked a little but I think this shows a basic shell for each color combination. Some of the cards might not fit that well, or you might want others too so I would encourage looking them over and tweaking them as you see fit. These are not necessarily the best lists possible, but they can give you ideas.
Your original build I think is just trying to do too much. CoCo is kind of expensive since the deck wants to be low to the ground. Rally and Return to the Ranks are fine as they can be powerhouses later in the game and win on the spot. I prefer Rally as it is an Instant and you are most likely going to want to sacrifice your stuff anyway so the Exile matters less. It also gets all creatures (except Messenger) for X=2 whereas Return only gets 2 creatures for X=2. And Return can't get Messenger back at all.
Some others, like Voice of Resurgence, just don't fit.
Doomed Traveler is seems like it would be fine as it gives you two creatures for 1 and it is low to the ground. Perhaps this could be in place of Messenger in the WB build. I just happen to like Messenger because, with at least one Artist or Cutthroat out, it represents 6 life loss on its own. And it can be a decent attacker/blocker as needed.
You mentioned you have an Aristocrats deck already and I find that, while they probably won't take down a GP, they have some power behind them for an FNM. Is this a playstyle you prefer? I had a mono-black deck built at one time and RB or WB aren't bad either and I enjoyed playing them.
What does your list look like for your current Aristocrats build?
4 Blood Artist
4 Zulaport Cutthroat
Sac Outlets
4 Viscera Seer
4 Bloodthrone Vampire
Recursive Creatures
4 Bloodghast
4 Bloodsoaked Champion
3 Geralf's Messenger
2 Tragic Slip
3 Fatal Push
3 Terminate
Utility
3 Kolaghan's Command
Lands
4 Bloodstained Mire
4 Polluted Delta
2 Urborg, Tomb of Yawgmoth
4 Blood Crypt
8 Swamp
4 Blood Artist
4 Zulaport Cutthroat
Sac Outlets
4 Viscera Seer
3 Bloodthrone Vampire
3 Cartel Aristocrat
4 Bloodghast
4 Bloodsoaked Champion
3 Geralf's Messenger
Recursion
3 Rally the Ancestors
Removal
2 Tragic Slip
3 Fatal Push
3 Path to Exile
4 Bloodstained Mire
4 Polluted Delta
2 Urborg, Tomb of Yawgmoth
4 Godless Shrine
8 Swamp
Obviously the numbers would be tweaked a little but I think this shows a basic shell for each color combination. Some of the cards might not fit that well, or you might want others too so I would encourage looking them over and tweaking them as you see fit. These are not necessarily the best lists possible, but they can give you ideas.
Your original build I think is just trying to do too much. CoCo is kind of expensive since the deck wants to be low to the ground. Rally and Return to the Ranks are fine as they can be powerhouses later in the game and win on the spot. I prefer Rally as it is an Instant and you are most likely going to want to sacrifice your stuff anyway so the Exile matters less. It also gets all creatures (except Messenger) for X=2 whereas Return only gets 2 creatures for X=2. And Return can't get Messenger back at all.
Some others, like Voice of Resurgence, just don't fit.
Doomed Traveler is seems like it would be fine as it gives you two creatures for 1 and it is low to the ground. Perhaps this could be in place of Messenger in the WB build. I just happen to like Messenger because, with at least one Artist or Cutthroat out, it represents 6 life loss on its own. And it can be a decent attacker/blocker as needed.
What does your list look like for your current Aristocrats build?