noFill()
Disables setting the fill color for shapes.
Calling noFill() is the same as making the fill completely transparent, as in fill(0, 0). If both noStroke() and noFill() are called, nothing will be drawn to the screen.
Examples

function setup()
size(100, 100)
background(200)
-- Draw the top square.
square(32, 10, 35)
-- Draw the bottom square.
noFill()
square(32, 55, 35)
describe('A white square above an empty square. Both squares have black outlines.')
end
Syntax
noFill()