We're plastering our walls in the livingroom with a mix of 1 part colored lime putty to 1 1/2 parts sand (the sand we are using is Kwikcrete Play Sand and has been screened so the granules are less than .5mm). This is the 3rd coat over blue board. But upon drying, parts of the wall are coarser than other parts, which would be okay, except the color is much darker in these areas, giving an unattractive and unwanted streakiness. Any guidance to why this is happening and how to solve it would be greatly appreciated.

Harvey

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...