G. Sarcone really makes great optical illusions. If you don’t believe me, just check some of his stuff we featured earlier. Take his “Neon Heart illusion” for example – can you see the faint glow surrounding the heart? It might help if you squint your eyes a little. Well, I’m afraid the neon glow you perceived is just an illusion, and that the yellow unicolor background is same for each box in the grid. It’s just the part of the grid painted black that’s responsible for this. I think it has something to do with contrasts, but don’t take me for granted. BTW, the effect gets much stronger the more you shrink the image. If you wish, you can download our desktop widget (if you haven’t already) and see how it looks in the “Illusion of The Day” widget.