Having guilt is physically and emotionally draining.
The apple's color, which was once red, has been "drained" out, leaving the apple with no color whatsoever.
The apple in this image has been drained of all its color, so it matches the plain background. The red, that was once on the apple, has been spread out on the "ground", with traces of it still on the bottom of the apple. This symbolizes how the original red, or characteristics of the apple, have been "drained" and removed. There's a lot more red color on the right side of the picture, as well as darker marks getting closer to the apple, portraying that the apple may have moved over time, representing the journey that a person with guilt would take, leaving behind more and more of their original, strong self over time. The plain, white background closely matches the new apple, illustrating the lack of uniqueness and plainness in the apple, meaning the personality has also been drained. The red, again, is prominent in this image, making the idea of the color (physical and mental characteristics) drained out of the object as the main focus.