1) Use software that has a color dropper so you can select the colored object and get its RGB values. Here's a simple, free, website where you can upload a photo, select the color, and it will return the RGB values. https://imagecolorpicker.com/
2) If the RGB values are not in decimal form, divide by 255. For example, if the RGB values are [56, 105, 137] then convert them to matlab's normalized values: rgb = [56, 105, 137] / 255;
3) set the color in your code: plot(x,y, 'color', rgb)
