The spinmap function shifts the colormap RGB values by some incremental value. For example, if the increment equals 1, color 1 becomes color 2, color 2 becomes color 3, etc.
spinmap(t,inc) rotates the colormap for approximately 10*t seconds and specifies an increment inc by which the colormap shifts. When inc is 1, the rotation appears smoother than the default (i.e., 2). Increments greater than 2 are less smooth than the default. A negative increment (e.g., –2) rotates the colormap in a negative direction.