Here's a solution
img = imread('Picture1.png');
imh = imshow(img);
% Create a mask using freehand ROI
h = imfreehand;
m = createMask(h, imh);
delete(h)
% Extract individual color channels
r = img(:,:,1);
g = img(:,:,2);
b = img(:,:,3);
% Get sum of intensity of each channel
r_s = sum(r(m));
g_s = sum(g(m));
b_s = sum(b(m));
% Calculate percentage of intensity of each color
r_p = r_s / (r_s + g_s + b_s) * 100;
g_p = g_s / (r_s + g_s + b_s) * 100;
b_p = b_s / (r_s + g_s + b_s) * 100;
