Working one colour into another is not as simple as stopping one colour, and then starting the next. When I shade through colours, I would possibly have four different colours/needles working together at the same time, but I would lessen the first colour, increase the second and third, and introduce a forth, before finishing the first, and then repeat . . . If one colour is worked, then stopped, then the next and stopped, and so on, the shading will be striped throughout, rather than softly and gradually shaded throughout. Blending tones of colour, the angle and length of stitch need to be considered also, especially when working around a curve.