If you remove your Graph Builder code, and add this code into your script, you will get your colors.
dt=current data table();
dt<<new column("Colors", ordinal,formula(If(:crack<=.003,1,2)));
dt << Graph Builder(
Size( 534, 464 ),
Show Control Panel( 0 ),
Variables( X( :Month ), Y( :Crack ), Color( :Colors ) ),
Elements( Points( X, Y, Legend( 3 ) ) ),
SendToReport(
Dispatch(
{},
"Crack",
ScaleBox,
{Min( 0.001 ), Add Ref Line( 0.003, "Dashed", "Dark Red", "", 1 )}
)
)
);
Jim