I wrote before about threads. This is a small sampler of four variegated threads I use routinely; three cotton, one rayon.
If you look at the samplers, you can see the Valdani and both Sulky threads have a long color change – there is a fair amount of each color on the thread. In close stitching, such as cobbling (small round circles) or small overlapping scribbles this long change gives depth and interest to the area covered. In lines, such as outlining or contouring or sketching, it means that the lines change color or character unless they are repeated, going back and forth over the line brings more different colors to it as well as making it a thicker line.
The King Tut, from Superior Thread, has a short color change, roughly every inch. This makes the thread read more like one color than several, as your eye averages the color within the area. I use these threads to blend different fabrics into a more cohesive mass. Because they are finer than the other threads, I also use them in the mid-ground and background of a piece.
I think the prettiest threads I use are the Sulky Blendable cottons – there are more different colors in one spool, and the patterns are more variable. I use these threads in the foreground of a piece, to keep details in the foreground from becoming an undifferentiated mass.
For a long time, I only knew of and used Sulky Rayon threads. They are easy to find, and come in many solid shades as well as the variegated versions. Rayon has a truly delightful sheen which is especially good for adding details and highlights to a subject, but it can get overwhelming in large areas.
Finding more variegated cotton threads, and variegations in different lengths, has helped my work evolve in a more painterly direction.