there might be either (without picture is hard to say)

pigment has not been completely mixed into/with the putty, little "clumps" are squished during application resulting in streaks.

to avoid that - it is not enough just to mix pigment with lime putty or mix with water and add to lime putty - pigment has to be ground with muller into a fine paste.

another reason could be the sand - Kwikcrete Play Sand might look fine and attractive - it is a bad sand for plastering - you need "plaster sand" for that - it is yellow to gray/umber color and very coarse in the bag...