#define _DELAY_ 150

void setup() {
    pinMode(PB0, OUTPUT);
    pinMode(PB1, OUTPUT);
    randomSeed(analogRead(A0));
}

byte fa=255, fb=0;

void loop() {
    fa = random(255);
    fb = random(255);
    //fa = 255-fa;
    //fb = 255-fb;
    analogWrite(PB0, fa);
    analogWrite(PB1, fb);
    delay(_DELAY_);
}