First of all I'd convert your image into an N-by-3 matrix.
rgbImage = imread('peppers.png');
[r, g, b] = imsplit(rgbImage);
rgbValues = [r(:), g(:), b(:)];
Then I'd use Classification Learner on the Apps tab of the tool ribbon. Tell it to start a new session using your rgbValues from the workspace. Then train it with the SVM classifier of your choice.
Finally, have the Classification Learner export the code to an m-file.
I'm attaching various demos that you might find interesting.