pellucid \puh-LOO-sid\ (adjective) - 1 : Transparent; clear; not opaque. 2 : Easily understandable.
"It was the first time he had seen her out of mourning, and above the pellucid eyes and the pencilled brows, on the dark hair, there was a small coronal of diamonds; swaying and scintillating as if a breath played about them." -- Frank Danby, 'Joseph in Jeopardy'
Pellucid comes from Latin pellucidus, "shining, transparent," from pellucere, "to shine through," from per-, "through" + lucere, "to shine."