Here is a simple modification of your script that will save residuals for both of your fits.
plot = data table("Correlation_Raw")<< Bivariate(
Y( :NewTester ),
X( :RefTester ),
Fit Line( {Confid Curves Fit( 1 ), Line Color( {212, 73, 88} )} ),
Fit Special( Intercept( 0 ), Slope( 1 ), {Line Color( {61, 174, 70} )}),
By( :Label )
);
bivRep = plot << Report;
plot << (Curve[1] << Save Residuals);
plot << (Curve[2] << Save Residuals);
See the Scripting Index for other examples
Help==>Scripting Index==>Bivariate==>Save Residuals
Jim