2D color map for error in a theoretical curve

Hi everybody:

I have recently done a programme in matlab which allows me to calculate a theoretical curve by changing the value (with slide bars) of a variable called nFlake_re and a different one named nFlake_im, and both variables together are needed to calculate a theoretical curve. I have a series of experimental values which I need to adjust the best I can to the theoretical curve by changing the values of both nFlake_re and nFlake_im until visually I see that the theoretical curve fits best with the experimental results.The problem is that there are many "correct" possibilities when doing this as, like I said, it all deppends on my opinion. Hence my question:

I would like to know if there is function to actually work out, for a range of values for nFlake_re and nFlake_im, the overall error of my experimental points (the same way for a linear regression you can calculate R^2 which represents how good the points fit the line)and plot this as a color map, being for example red a really bad fit of the theoretical line to the experimental results, and blue being the best fit of the points.

This will create a 2D map where there will be several possible regions of values of nFlake_re and its corresponding nFlake_im where the fit is best.

Thanks to anybody who can help me with this.

Guillermo