How can I select a specific region of a color diagram?

Hi; I have a gamma-corrected RGB matrix, obtained by computing the chromaticity matrices to the RGB 709 transformation matrix. I did the following to display the color diagram:

img = Corr_rgb;

    figure;
    image([0:.005:1],[0:.005:1],img);
    axis('xy');

where Corr_rgb is the gamma-corrected RGB matrix. Now I want to insert the chromaticity diagram to show the colors inside the RGB 709 gamut. I know how to insert the chromaticity diagram into the color diagram, but how can I make the plot to show only the colors inside the RGB 709 gamut so I can have a color-filled triangle as a final result?