Code
size (500,500);
background (150,150,150);
smooth ();
noStroke();
int spacing = 15;
for (int x=width/10; x<width; x+=width/5) {
for (int y=height/10; y<height; y+=height/5) {
for (int target=90; target>=15; target-=spacing) {
fill (255-(target*2.83));
ellipse (x,y, target,target);
}
}
}
0205 - Gradual buildup of a complex design: Another for{} loop
Statement:Add yet another repetition structure around the previous assignment, in order to create the design shown here: 
If you've done this correctly, step back and take a look at that - you've made a triple for{} loop!