dt=Open("$SAMPLE_DATA/Big Class.jmp");dt[1,1] is set to red
dt[1,2] is set to white
dt[1,1] is set to clear coloring
Thanks!
One to do this is to set the colors of cells in your table manually. Then look at the table script. Right click on the red triangle next to the table name and select Copy table script:

Here's the resulting code:
New Table( "Untitled 26", Add Rows( 3 ),
New Column( "Column 1", Numeric, "Continuous",
Format( "Best", 12 ),
Color Cells( {{73, {1}}, {74, {2}}} ),
Set Values( [1, 2, 3] )
),
New Column( "Column 2", Character, "Nominal",
Color Cells( {{75, {2}}, {67, {3}}} ),
Set Values( {"a", "b", "c"} )
)
)