Jason's

size(400,400);
background(0);
strokeWeight(2);
for (int y = 0; y < 400; y += 10) {
for (int x = 0; x < 400; x += 10) {
  stroke(0,x*0.8,y*0.2);
fill(140,x*0.3,y*0.4);
rect(x, y, 10, 10);
}
}

size(400,400);
background(0);
strokeWeight(2);
for (int y = 0; y < 400; y += 20) {
for (int x = 0; x < 400; x += 20) {
  stroke(0,x*0.8,y*0.2);
fill(140,x*0.3,y*0.4);
rect(x, y, 10, 10);
}
}

size(400,400);
background(0);
strokeWeight(2);
for (int y = 0; y <= 400; y += 20) {
for (int x = 0; x <= 400; x += 20) {
  stroke(0,x*0.8,y*0.2);
fill(140,x*0.3,y*0.4);
rect(x, y, 10, 10);
rect(x,y+10,10,10);
}
}

size(400,400);
background(0);
strokeWeight(2);
for (int y = 0; y <= 400; y += 20) {
for (int x = 0; x <= 400; x += 20) {
  stroke(0,x*0.8,y*0.2);
fill(140,x*0.3,y*0.4);
rect(x, y, 10, 10);
rect(-10+x,y,10,10);
}
}

size(400,400);
background(0);
strokeWeight(2);
for (int y = 0; y <= 400; y += 20) {
for (int x = 0; x <= 400; x += 20) {
  stroke(0,x*0.8,y*0.2);
fill(140,x*0.3,y*0.4);
rect(x, y, 10, 10);
rect(-10+x,10+y,10,10);
}
}