If you are playing around with the color schemes, you may notice that some color schemes have 5 color buckets in the palette, while others have 6 color buckets.
So, what happens when you switch from a 5-bucket color scheme to a 6-bucket color scheme and vice-versa?
The 5 colors from the first scheme will switch to the corresponding 5 colors of the second scheme, and the 6th color of the 2nd scheme would not be used in the visual. However, once you switch to the 2nd color scheme, you can associate any object with the 6th color of the 2nd scheme by choosing the color in the color picker tool, in the top toolbar.
If your existing color scheme has 6 color buckets and you switch to a scheme that only 5 color buckets, then the objects that were associated with the 6th color bucket from the first color scheme will continue to retain their color, even after you switch to a scheme that has lesser number of buckets.
If you switch from a 6-color scheme to a 5-color scheme and then change back to a different 6-color scheme, the 6th bucket of the current applied scheme will be set and will not be the original bucket's 6th bucket color.