Figure 6.

Reversible color tuning by swelling. A glass substrate coated with a soft opal film was dipped in a hydrophobic liquid, octane. In the photograph (right) , the dry area has the initial blue color and the wet area is red. The color is reverted from red to blue by evaporating the octane. The model (left) shows how the spacing between colloidal particles is changed by the swollen PDMS elastomer from d₁ to d₂.