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No problem :) I re-read your question and I think I understand now. Basically the dark shapes that you see on insect's eyes sometimes are an optical effect due to the structure of the ommatidia and the way that light strikes them and then is reflected back to the observer.

You can think of each ommatidium as a transparent cylinder and thousands of similar cylinders are packed together but, as the eye surface curves each cylinder points in a slightly different direction to its neighbours. Generally speaking, light is either bounced off the ommatidia up to your eye (giving you the impression of colour) or when you are looking down directly into the ommatidia it vanishes down into the cylinder and doesn't bounce back out (giving you a black/dark patch). :)