I wonder if the issue is perhaps in how you are using the colors in your images. Can you describe a bit more about what you are doing? What properties pertaining to color and transparency are you setting? Is this something that occurs when you overlap two images that otherwise work?
Coming up with a nice lime green or bright pink that will be noticeable if it “leaks” into the graphic shouldn’t be the issue. You can pick them from a palette or color tool and observe the RBG channel values. Then include an alpha-channel value of 0. (RGBA with A = 0). In truth, any color with the alpha-channel set to 0 should behave properly and not adversely affect other colors.