Code for fading RGB via color map.

rgbFadeLEDTessel.js

var five = require("johnny-five"),
    TesselIO = require("tessel-io"),
    board = new five.Board({
      io: new TesselIO()
    });

// Initial Red color to start with. 
// Decent transitions are easier with RGB vs HEX. 
var startingColorObject = {
  r: 255,
  g: 0,
  b: 0
}

board.on("ready", function() {
  var index = 0,
      // On tessel 2 the pins have a port prefix when using with johnny-five
      RGBLED = new five.Led.RGB({
        pins: {
          red: "A5", // PWM Pin
          green: "A6", // PWM Pin
          blue: "B5" // PWM Pin
        },
        isAnode: true
      });

  function fadeFromGreenToRed() {
    for(var i=0; i<255; i++) {
      startingColorObject.r = i;
      startingColorObject.g = 255-i;
      startingColorObject.b = 0;
      RGBLED.color(
        rgbToHex(startingColorObject)
      );
    }
  }

  function fadeFromRedToBlue() {
    for(var i=0; i<255; i++) {
      startingColorObject.r = 255-i;
      startingColorObject.g = 0;
      startingColorObject.b = i;
      RGBLED.color(
        rgbToHex(startingColorObject)
      );
    }
  } 

  function fadeFromBlueToGreen() {
    for(var i=0; i<255; i++) {
      startingColorObject.r = 0;
      startingColorObject.g = i;
      startingColorObject.b = 255-i;
      RGBLED.color(
        rgbToHex(startingColorObject)
      );
    }
  }

  // Handles conversions back to hex where the ending '0' would be missing.
  function componentToHex(c) {
      var hex = c.toString(16);
      return hex.length == 1 ? "0" + hex : hex;
  }

  function rgbToHex(rgbObject) {
      var r = rgbObject.r,
          g = rgbObject.g,
          b = rgbObject.b;
      return "#" + componentToHex(r) + componentToHex(g) + componentToHex(b);
  }
  
  function rgbFade() {
    fadeFromRedToBlue();
    fadeFromBlueToGreen();
    fadeFromGreenToRed();
  }

  // Set light to initial color. 
  RGBLED.color(
    rgbToHex(startingColorObject)
  );

  setInterval(rgbFade);
});