Colours look great. i think it also needs a little more light. I may suggest to increase that f/stop for 2 reasons, the first is that even with 13 images your final slice of critical focus for the stack may be too shallow to capture all you want as sharp as you like and the second is generally speaking no lens is at its best at its lowest or highest setting (aparture or f/stop in this case). If you absolutely need that light or depth of field use f/1.8 but I can almost guarantee it will be sharper and have better results at f 2.8 and above, the questions is can you get that light back from somewhere else..