Try this:
% I have true color image (looks gray though because it is ultrasound image). I read the image.
im = imread('peppers.png');
subplot(2,2,1);
imshow(im);
% Convert the image into gray scale.
I = rgb2gray(im);
subplot(2,2,2);
imshow(I);
% Then ind2rgb
rgbImage = uint8(255 * ind2rgb(I, jet(256)));
subplot(2,2,3);
imshow(rgbImage);
% Set up figure properties:
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);
% Get rid of tool bar and pulldown menus that are along top of figure.
set(gcf, 'Toolbar', 'none', 'Menu', 'none');
% Give a name to the title bar.
set(gcf, 'Name', 'Demo by ImageAnalyst', 'NumberTitle', 'Off')
