Color effect with fastled, please help.

Hi guys, I would like to create a rainbow effect with fastled using the ws2812b rgb strip (95 led)

Basically I have this sketch that creates some cool effects.

  //EFFECT RAINBOW
  if (effectString == "rainbow") {
    // FastLED's built-in rainbow generator
    static uint8_t starthue = 0;    thishue++;
    fill_rainbow(leds, NUM_LEDS, thishue, deltahue);
    if (transitionTime == 0 or transitionTime == NULL) {
      transitionTime = 130;
    }
    showleds();
  }


  //EFFECT RAINBOW WITH GLITTER
  if (effectString == "rainbow with glitter") {               // FastLED's built-in rainbow generator with Glitter
    static uint8_t starthue = 0;
    thishue++;
    fill_rainbow(leds, NUM_LEDS, thishue, deltahue);
    addGlitter(80);
    if (transitionTime == 0 or transitionTime == NULL) {
      transitionTime = 130;
    }
    showleds();
  }

how can I create a rainbow that doesn't move over the leds but that shifts color on all leds at the same time. basically I want to have a slow transition over all the colors on all leds at the same time. can you help me creating this effect please?