Colour by Nimbus

A small, thin-walled ball is created, and filled with powdered biodregradable dye. The wall thickness is important as it determines the balls strength. At a certain reduction in atmospheric pressure, the ball will burst, releasing its powdered dye into the immediate environment. But they are light - the size of the balls has been determined to optimise their flying efficiency.
The artist selects his payload from a wide variety of colours and wall thicknesses - will he go for layers of colour, or a more esoteric effect?
The large bag of balls is tied to the plane, and it begins it's treacherous journey toward the thunderstorm. As it reaches the base of the cloud, the balls are slowly released from the bag a few at a time. The overpowering upcurrent of the cumulo-nimbus drags the lightweight spheroids upwards, like the hailstones already building within the cloud.
The payload is delivered. Gradually, as the upcurrent grows stronger and the circulation more powerful, the balls begin to burst as they reach the altitude at which they can no longer contain their colourful contents. Water condenses around the particles creating coloured mist in that area of the cloud.
From a distance, the cloud gradually begins to change colour, with layers of blue and red, pink and all the colours the artist has chosen. But the picture is painted by mother nature, and falls to earth as coloured rain, to degrade in the drains as the thunderstorm passes.