deke.com posts about translucency

Painting with Gradients and Translucency in Adobe Illustrator

Deke colors his face made of triangles with custom gradients and varying opacity.

Photoshop Top 40, Feature #11: Opacity and Blend Modes

Changing the Opacity is like mixing a cocktail with, say, 25% active layer and 75% all layers below. Assigning a blend mode is like shining a light or casting a shadow: The active layer infuses those behind it with life.