I was trying to display a shadding-off with two colors
and i made an error that I'd like to share with you.
Just copy this code in a sketch. (You need to create a font).

void setup(){
size(600, 510);noStroke();background(100);
PFont f = loadFont("CenturyGothic-Bold-48.vlw");  //Arial-BoldMT-48.vlw");
textFont(f,16);
}
void draw() {
background(100);fill(0);
text("// richard Monnier, école d'art d'Annecy.",110,80); text("// a misuse of color variable",110,20);text("// that yields more surprises",110,40);text("// than a right use of a random function",110,60);

color a = color(mouseY/2, 0, 0);fill(a);String rou = str(a);
text("color COLOR1 = color(mouseY, 0, 0);        //result :" + rou,110,120);
color b = color(0, 0, mouseY/2);fill(b);String bleu = str(b);
text("color COLOR2 = color(0 ,0 ,mouseY);             //result :" + bleu,110,140);
fill(0);
text(" for(int i = 1; i<height; i=i+1",110,180);
text(" { ",110,200);
text("// Here it is the use of the color variable as a common number : ",110,220);
text(" fill ((( COLOR1 + COLOR2 )/height)*i);",110,260);

for(int i=1; i<255; i=i+1) {
fill(((a+b)/255)*i);
rect(0,i*2,100,(i*2)+2);    }  
fill((a+b)/height); String unit = hex((a+b)/height);

text("// fortunately, Processing find a color in this result: " + unit,110,300);
text(" rect(0,i,100,i+1);                              //displaying the color",110,340);
text(" } ",110,360);