The cheese is a lighter yellow and appears in a neat square. The mustard is a golden yellow and appears as a messy squiggle. The ketchup/tomatoes are very close in color, but the first has rounded edges and the second is again a messy squiggle.
Working more off shape than color has been helpful for me on my phone. You can also look at placement...cheese is usually directly underneath or above meats, condiments are usually the top-most ingredient, etc.