this problem is actually a part of a more complex code, but i was to lazy to explain and didn't want to bother you all.
:)

Just use a variable to store the background color.

Code Example

1. color bg;
2.  
3. void setup() {
4.   size(500, 500);
5. }
6.  
7. void draw() {
8.   background(bg);
9.   if (mouseX >= 250) { bg = color(random(255), random(255), random(255)); }
10.   line(250, 0, 250, height);
11. }

I thought the explained way  would help me, but i was wrong.
I won't get along without posting the code.

So I wrote a  function which writes text in randomly altering fonts, but the function shall run at start once.
Then the textfont shall only change if i am in the textfield.

/////////////////////////////////////////////////////////////////////////////////////////////////

1. PImage grad;
   
   
   //Counter
   
   int zahl;
   int richtung;
   
   
   //trig
   
   int angle = 50;
   
   float transX;
   float transY;
   
   float wGrad;
   float hGrad;
   
     color c1 = color(255, 0, 0);
     color c2 = color(0, 255, 0 );
   
   PFont[] fontList = new PFont[2];
   float linelength;
   float abstand;
   float fontPosX = 0;
   int fontPosY = -250;
   int fontSize = 50;
   float linienAbstand;
   float xPos;
   float corrY = 2;
   
   
   void setup() {
   
     size(800, 600);
    
     smooth();
     background(255);
   
     fontPosX = fontSize*.86;
   
     linienAbstand = fontSize* .5;
   
     xPos = width/2;
    
   
   
     fontList[0] = loadFont("AntiqueOlive-Roman-70.vlw");
     fontList[1] = loadFont("Imago-Book-70.vlw");
    
   
   
       //TRIG For the Gradient
   
     transX = (sin(radians(90-angle)))*(sin(radians(angle))*height);
     transY = (cos(radians(90-angle)))*(sin(radians(angle))*height);
   
     hGrad = (sin(radians(angle)) * width)+(cos(radians(angle))*height);
     wGrad = (cos(radians(angle)) * width)+(sin(radians(angle))*height);
   
   
   ////// INIT COUNTER //////
   
    richtung = -1;
    zahl = 500;
   
   }
   
   
   
   
   
   void draw() {
   
     rectMode(CORNER);
   
     translate(-transX, transY);
   
     rotate(radians(-angle));
   
   
     //////////////////
   
     grad = generateGradient(c1, c2, (int) wGrad, (int) hGrad);
   
     ///////////
   
     image(grad, 0, 0);
   
     fill(255, 200);
     noStroke();
   
     rect(0, 0, width*2, height*2);
    
      rotate(radians(angle));
   
   
   ////// POSITION where the Randomness begins /////
   
     if((mouseX <= 481) && (mouseX >= 134)) {
       if((mouseY >= 80) && (mouseY<= 134))  {
          runBaby();
         }
     }
   
   }
   
   
   void runBaby() {
   
    
     //////COUNTER///////////
   
   
   if (richtung == -1){
               zahl=zahl-10;
                 if (zahl == 0){
                   richtung = 1;
                 }
               }
              
               if (richtung == 1){
               zahl=zahl+10;
                 if (zahl == 500){
                   richtung = -1;
                 }
               }
   
   
   ////////
    
     rectMode(CENTER);
     fill(0);
   
    
   
   
   ///////////// LETTERS
   
     int  x = (int)random(0, 2);
     // println(x);
     textFont(fontList[x], fontSize);
     // textFont(fontList[zeitSchleife], fontSize); 
   
     textAlign(CENTER, CENTER);
     text("F", xPos + fontPosX, fontPosY);
   
   
     x = (int)random(0, 2);
     // println(x);
     textFont(fontList[x], fontSize);
     // textFont(fontList[zeitSchleife], fontSize);
     text("R", xPos + 2*fontPosX, fontPosY);
   
   
     x = (int)random(0, 2);
     // println(x);
     textFont(fontList[x], fontSize);
     // textFont(fontList[zeitSchleife], fontSize);
     text("O", xPos +  3*fontPosX, fontPosY);
   
   
     x = (int)random(0, 2);
     // println(x);
     textFont(fontList[x], fontSize);
     // textFont(fontList[zeitSchleife], fontSize);
     text("U", xPos +  4*fontPosX, fontPosY);
   
   
     x = (int)random(0, 2);
     // println(x);
     textFont(fontList[x], fontSize);
     // textFont(fontList[zeitSchleife], fontSize);
     text("T", xPos +  5*fontPosX, fontPosY);
   
   
     x = (int)random(0, 2);
     // println(x);
     textFont(fontList[x], fontSize);
     // textFont(fontList[zeitSchleife], fontSize);
     text("E", xPos +  6*fontPosX, fontPosY);
   
   
     x = (int)random(0, 2);
     textFont(fontList[x], fontSize);
   
     text("6", xPos +  7*fontPosX+15, fontPosY-corrY);
   
   
     x = (int)random(0, 2);
     textFont(fontList[x], fontSize);
   
     text("6", xPos +  8*fontPosX+15, fontPosY-corrY);
   
   
   }
   
   
   // Generate a vertical gradient image
   PImage generateGradient(color top, color bottom, int w, int h) {
     int tR = (top >> 16) & 0xFF;
     int tG = (top >> 8) & 0xFF;
     int tB = top & 0xFF;
     int bR = (bottom >> 16) & 0xFF;
     int bG = (bottom >> 8) & 0xFF;
     int bB = bottom & 0xFF;
   
     PImage bg = createImage(w, h, RGB);
     bg.loadPixels();
     for (int i=0; i < bg.pixels.length; i++) {
       int y = i/bg.width;
       //float n = y/(float)bg.height;
       // for a horizontal gradient:
       float n = y/(float)bg.width;
      
       bg.pixels[i] = color(
       lerp(tR, bR+zahl, n),
       lerp(tG, bG+zahl, n),
       lerp(tB, bB, n),
       255);
     }
     bg.updatePixels();
     return bg;
    
   }
   

///////////////////////////////////////////////////////////////////////////////////////////////////



Is there a way to do it by code?
loop - noLopp doesnt make sense for me.



PS: To run the sketch you should create 2 fonts ("XXXXX.vlw") and insert them instead of mine in the fontList Array, afterwards move the mouse in the in the textfield. near the upper left corner.


AND PLEEEEASE HELP ME.

Thats amazing how you have shortened the script, thanks alot for the transfer. Now I will Sleep well;)
In Fact it looks quite the same, I couldnt have imagine. And learned some new Textstuff. Great.

Hey
I got the whole thing in this post worked out as i wanted, but there is still one thing i dont get.

How can I generate Random Values and store them only if they havent been generated before.
How would you code that?