Red is a Super Soul, Blue is a Recovery Item and Yellow is Clothing for a reward. I am going to make a list with the Buus I create but my guess is the rewards are given at Random. If you are a Buu you can have 10 but if you are anything else you get 6 Buus. In order to get the little Buus moving you have to feed them once, feeding them 5 times changes their color. After you do a few missions they will return and you can collect your item. When the Buu gives you an option to Guard or Calm down it means it can change color. If you Guard it will change and if you Calm it down it will remain the same.
Red Rewards
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You can get repeats of the Super Souls, I did on my third run. I thought giving them different food would change results but so far that hasn’t been the case.
That Looks Fun! Super Soul – Goten’s Super Soul – Always boosts movement speed and when at max Stamina your melee skills do more damage, Power Ki blast.
I won’t Use My Full Power Yet – Kibito’s Super Soul- Cures Ally Status Ailments, Recovers Ki(M) and Recvoers Stamina(M), activates when a Reinforcement Skill happens.
I’m Still Not Used To This Form – Super Saiyan 3 Goku Super Soul – Boosts Ki Blasted based skills(L) but drains Ki, must be Super Saiyan or Golden mode for this to activate.
Yellow Rewards
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You can also get repeats here.
Ninja Suit(Demon) – Raises Stamina and Ki but lowers Strike supers.
Vegeta Normal Clothes – Boosts Stamina and Ki but lowers HP.
elite Suit Demon – Raises all stats but Ki and Ki Blast Supers, lowers them.
Blue Rewards
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These are all sorts of different recovery items, I don’t use the blue ones much.