PFont label;
void setup(){
   size(200,100); 
   background(255);
   label = createFont("SansSerif",15);
   textFont(label);
   setButton(0,255);
   
}
void draw(){
}
void mousePressed(){
  if(mouseX > 10 && mouseX < 90 && mouseY > 10 && mouseY < 40){
     setButton(200,30);
  }
}
void mouseReleased(){
  if(mouseX > 10 && mouseX < 90 && mouseY > 10 && mouseY < 40){
     setButton(0,255);
  }
}
void setButton(color col1,color col2){
   noStroke();
   fill(col1);
   rect(10,10,80,30);
   
   fill(col2);
   textAlign(CENTER,CENTER);
   text("Button",50,22);
}