If you look around in the neighbouring figure you will notice the appearance and disappearance of black dots at the crossings.
Even though this figure looks similar to the Hermann-Grid, it is markedly more vivid. Furthermore, the effect is probably caused by different mechanisms than those causing the Hermann-Grid effect.
Question: Do the streets or the squares influence the colour of the apparent disks?
As you notice in the neighbouring figure, red streets leave the disks black. But if the squares are red (move mouse over figure), the disks acquire a reddish tint...
Schrauf M, Lingelbach B, Lingelbach E & Wist ER (1995) The Hermann grid and the scintillation effect. Perception 24: suppl, 88–89
Schrauf M, Lingelbach B & Wist (1997) The scintillating grid illusion. Vision Res 37:1033–1038
Advice by Bernd Lingelbach gratefully acknowledged.