In JMP I find that if I add cell colors by selecting the cells, right clicking, and doing "Color Cells", then there doesn't seem to be any way to remove the colorings. Even if I try to use the "Color or Mark by Column" function or the "Value Colors" property to change the colorings of the cells, it seems to be unable to overwrite the custom colorings. Doing "Clear Row States" does not get rid of the custom colorings. Isn't there a way to remove the custom cell colorings?
A little late to the party, but the one exception to the above I found is that if you color all of the cells in a column in one operation (select 1 or more columns, select ALL rows, right click and color), then add a new row, you'll see the new row has inherited the column's color. You can successfully change any cell or group of cells in this column to any other color, but when you try to color it black again, it goes to whatever color you initially selected when you colored the whole column. I got around this by coloring the cells white. It is not exactly the same but for my purposes is close enough.
If you highlight the first half of the rows and color it red, then the 2nd half and color it red, this doesn't happen.
The above is true whether you do it in a script or via the right click menu.