Ich habe ein RGB LED mit Common Anode benutzt.

Das heist der Common, das ist der längste Anschluss kommt an Plus. Die 3 Farben kommen an die Ausgänge des Arduinos.
Das Programm stammt aus dem Netz. Esist sehr aufwendig aber funktioniert gut, das gesammte Farbsprktrum wird durchlaufen. Vieleicht mach ich mir mal die Mühe und schreibe selbst eins.

 

// Output
int redPin = 9;   // Rotes LED,   an  digital pin 9
int grnPin = 10;  // Günes LED, an digital pin 10
int bluPin = 11;  // Blaues LED,  an  digital pin 11
// Color arrays
int black[3]  = { 0, 0, 0 };
int white[3]  = { 100, 100, 100 };
int red[3]    = { 100, 0, 0 };
int green[3]  = { 0, 100, 0 };
int blue[3]   = { 0, 0, 100 };
int yellow[3] = { 40, 95, 0 };
int dimWhite[3] = { 30, 30, 30 };
// etc.
// Set initial color
int redVal = black[0];
int grnVal = black[1]; 
int bluVal = black[2];
int wait = 10;      // 10ms internal crossFade delay; increase for slower fades
int hold = 0;       // Optional hold when a color is complete, before the next crossFade
int DEBUG = 1;      // DEBUG counter; if set to 1, will write values back via serial
int loopCount = 60; // How often should DEBUG report?
int repeat = 3;     // How many times should we loop before stopping? (0 for no stop)
int j = 0;          // Loop counter for repeat
// Initialize color variables
int prevR = redVal;
int prevG = grnVal;
int prevB = bluVal;
// Set up the LED outputs
void setup()
{
  pinMode(redPin, OUTPUT);   // sets the pins as output
  pinMode(grnPin, OUTPUT);   
  pinMode(bluPin, OUTPUT); 
  if (DEBUG) {           // If we want to see values for debugging...
    Serial.begin(9600);  // ...set up the serial ouput 
  }
}
// Main program: list the order of crossfades
void loop()
{
  crossFade(red);
  crossFade(green);
  crossFade(blue);
  crossFade(yellow);
  if (repeat) { // Do we loop a finite number of times?
    j += 1;
    if (j >= repeat) { // Are we there yet?
      exit(j);         // If so, stop.
    }
  }
}
/* BELOW THIS LINE IS THE MATH -- YOU SHOULDN'T NEED TO CHANGE THIS FOR THE BASICS
* 
* The program works like this:
* Imagine a crossfade that moves the red LED from 0-10, 
*   the green from 0-5, and the blue from 10 to 7, in
*   ten steps.
*   We'd want to count the 10 steps and increase or 
*   decrease color values in evenly stepped increments.
*   Imagine a + indicates raising a value by 1, and a -
*   equals lowering it. Our 10 step fade would look like:
* 
*   1 2 3 4 5 6 7 8 9 10
* R + + + + + + + + + +
* G   +   +   +   +   +
* B     -     -     -
* 
* The red rises from 0 to 10 in ten steps, the green from 
* 0-5 in 5 steps, and the blue falls from 10 to 7 in three steps.
* 
* In the real program, the color percentages are converted to 
* 0-255 values, and there are 1020 steps (255*4).
* 
* To figure out how big a step there should be between one up- or
* down-tick of one of the LED values, we call calculateStep(), 
* which calculates the absolute gap between the start and end values, 
* and then divides that gap by 1020 to determine the size of the step  
* between adjustments in the value.
*/
int calculateStep(int prevValue, int endValue) {
  int step = endValue - prevValue; // What's the overall gap?
  if (step) {                      // If its non-zero, 
    step = 1020/step;              //   divide by 1020
  } 
  return step;
}
/* The next function is calculateVal. When the loop value, i,
*  reaches the step size appropriate for one of the
*  colors, it increases or decreases the value of that color by 1. 
*  (R, G, and B are each calculated separately.)
*/
int calculateVal(int step, int val, int i) {
  if ((step) && i % step == 0) { // If step is non-zero and its time to change a value,
    if (step > 0) {              //   increment the value if step is positive...
      val += 1;           
    } 
    else if (step < 0) {         //   ...or decrement it if step is negative
      val -= 1;
    } 
  }
  // Defensive driving: make sure val stays in the range 0-255
  if (val > 255) {
    val = 255;
  } 
  else if (val < 0) {
    val = 0;
  }
  return val;
}
/* crossFade() converts the percentage colors to a 
*  0-255 range, then loops 1020 times, checking to see if  
*  the value needs to be updated each time, then writing
*  the color values to the correct pins.
*/
void crossFade(int color[3]) {
  // Convert to 0-255
  int R = (color[0] * 255) / 100;
  int G = (color[1] * 255) / 100;
  int B = (color[2] * 255) / 100;
  int stepR = calculateStep(prevR, R);
  int stepG = calculateStep(prevG, G); 
  int stepB = calculateStep(prevB, B);
  for (int i = 0; i <= 1020; i++) {
    redVal = calculateVal(stepR, redVal, i);
    grnVal = calculateVal(stepG, grnVal, i);
    bluVal = calculateVal(stepB, bluVal, i);
    analogWrite(redPin, redVal);   // Write current values to LED pins
    analogWrite(grnPin, grnVal);      
    analogWrite(bluPin, bluVal); 
    delay(wait); // Pause for 'wait' milliseconds before resuming the loop
    if (DEBUG) { // If we want serial output, print it at the 
      if (i == 0 or i % loopCount == 0) { // beginning, and every loopCount times
        Serial.print("Loop/RGB: #");
        Serial.print(i);
        Serial.print(" | ");
        Serial.print(redVal);
        Serial.print(" / ");
        Serial.print(grnVal);
        Serial.print(" / ");  
        Serial.println(bluVal); 
      } 
      DEBUG += 1;
    }
  }
  // Update current values for next loop
  prevR = redVal; 
  prevG = grnVal; 
  prevB = bluVal;
  delay(hold); // Pause for optional 'wait' milliseconds before resuming the loop
}