The Rect() graphics function can create such colored areas. Be sure to call Rect() before the Marker() function so that the colors do not obscure the points.
Example:
Names Default to Here( 1 );
dt = Open( "$SAMPLE_DATA/Big Class.jmp" );
obj = dt << Bivariate(
Y( :weight ),
X( :height ),
Fit Line( {Line Color( {212, 73, 88} )} ),
SendToReport(
Dispatch(
{},
"Bivar Plot",
FrameBox,
{Add Graphics Script(
4,
Description( "" ),
Fill Color( "blue" );
Rect( 50, 120, 60, 60, 1 );
)}
)
)
);