Degradados

float posx;
float posy;

void setup (){

size (500,300);
background (0);
}

void draw(){

int rojo =40;
int posY =10;

while (rojo<= 230){
fill(rojo, 0,0);
rect(50, posY, 200,20);

rojo= rojo+20;
posY= posY + 30;

}
}

Degradado negro-rojo

Negro - rojo

void setup()
{

size (500 , 300);
background(0);
}

void draw()
{
int rojo = 230;
int posX=20;
int posY=20;

while(rojo >= 20)
{
fill (rojo,0,0); rect(posX,posY,20,20);

rojo =rojo -2;
posX = posX +25;

if (posX>=250)
{
posY=posY+25;
posX=20; } }

}

Piramidal

void setup()
{

size (500 , 300);
background(0);
}

void draw()
{

int verde = 80;
int posX=20;

while(verde <= 230)

{
fill (0,verde,0);
rect(posX,20,20,200);

verde =verde + 20;
posX = posX+30;

}
}

Verde - negro

void setup (){

size (500,300);
background (255);
}
void draw()
{
int blanco =0;
int posX=20;
int posY=20;

while (blanco <=500){

fill (256,256,256);
rect(posX, 0,0,height);
rect(0,posY,width,0);

blanco= blanco+20;
posX= posX +20;
posY= posY +20;
}
}