Change letter fill on hover

float bx;
float by;
float ax;
float ay;
boolean overA = false;
boolean overB = false;
PFont f;

void setup() {
  size(640, 360);
  ax = 80;
  ay = 80;
  bx = 160;
  by = 80;
  f = createFont("Arial",20,true);
}

void draw() {
  background(0);
  textFont(f);

  char a = 'X';
  char b = 'D';
  float cwA = textWidth(a);
  float cwB = textWidth(b);

  // Text A
  if (mouseX > ax-cwA/2.0 && mouseX < ax+cwA/2.0 &&
      mouseY > ay-2*cwA && mouseY < ay) {
    overA = true;
    fill(200);
  } else {
    fill(255);
    overA = false;
  }
  text(a, ax-cwA/2.0, ay-cwA/2.0);

  // Text B
  if (mouseX > bx-cwB/2.0 && mouseX < bx+cwB/2.0 &&
      mouseY > by-2*cwB && mouseY < by) {
    overB = true;
    fill(200);
  } else {
    fill(255);
    overB = false;
  }
  text(b, bx-cwA/2.0, by-cwB/2.0);
}