Processing II

Código fonte

void setup ()
{
background(178, 11, 11);
size (600, 600);
smooth();
stroke (10);
}
void draw ()
{
ellipse (mouseX, mouseY, 100, 100);
if (mousePressed == true)
{
fill(mouseX);
}
else
{
fill(mouseY);
}
ellipse(mouseX, mouseY, 50, 50);
}

Resultado: