This is my original image:

But when I load it up on MATLAB and use ims
GIF is indexed format, and each image can have its own colormap. So you need to read the colormap together with the image:
[I, Imap] = imread('D:\Matty\pout.gif');
imshow(I,Imap)
I've tested it on your image and it works very well. i don't understand what was the problem @Lucas described in his answer.