Do you know the exact proportions in which you mixed the reagents: CuSO4, NH3, and KI?
My guess is that the basic copper sulfate is responsible for the color, and also the product of CuI oxidation by oxygen from the air in the presence of water.
Well, the (Cu(NH3)4)SO4 was from a previous experiment, (CuSO4 + NH4OH, then precipitated with methanol), I then filtered it and dried it. I dont know how pure it is, but honestly it must be good enough since the powder was crystalline. I dont think there was much copper sulfate remaining, i washed it with lots of methanol/ammonia to make sure it's as pure as it can be (might need a recryst. though).
And for the KI... I didn't really write down how much I used, since it was just to see if there was a reaction. I think it was like 20g in 100ml of water ? Mixed with maybe 5g of the copper-ammonia complex in 100ml of water. I don't really remember and I don't have enough KI to redo the experiment, might have to order some.