Spark firmware for setting RGB LED color using the Spark Tinker mobile app's analogWrite on pins A4, A5, and A6.

application.cpp

// Default to pinkish
int redValue = 255;
int greenValue = 33;
int blueValue = 121;

int countdown;

void showColor() {
  RGB.control(true);
  RGB.color(redValue, greenValue, blueValue);
  countdown = 1000;    
}

int updateRGBLEDColor(String pinAndValue) {
  int pinNumber = pinAndValue.charAt(1) - '0';
  int value = pinAndValue.substring(3).toInt();

  if (4 == pinNumber)
    redValue = value;
  else if (5 == pinNumber)
    greenValue = value;
  else if (6 == pinNumber)
    blueValue = value;

  showColor();

  return 0;
}

void setup() {
  Spark.function("analogwrite", updateRGBLEDColor);
  showColor();
}

void loop() {
  if (0 == countdown)
    RGB.control(false);

  if (0 <= countdown)
    --countdown;
}