Arduino RGB led-strip turns off at full intensity

Question

I'm playing around with an Arduino Uno, and an RGB led-strip (Ikea Dioder 4 strips, only one is connected). Primary and secondary colors look fine when writing 255 to one or two colors. The problem is when I want white light (e.g. 255 on all three LEDs), then instead of becoming fully white, it just turns off.

I have an ethernet-shield connected to the Arduino, and a seperate 12V dc powersource. When I connect the power source to the Arduino, it works, but the regulator gets insanely hot (known issue). So I connect the LEDs to the 12V power source directly (they are rated at 12V, the Ikea one is also 12V). Only this causes the problem.

In the program below I can see it very clearly. The code should do the following: fade to red; fade to yellow; fade to white; repeat. The first two go fine, but when it's time to fade to white, it fades to black instead. It just turns off. And I have no idea why.

int redPin = 3;
int greenPin = 5;
int bluePin = 6;
int color[] = {3, 5, 6};
int i = 0;
int j = 0;

void setup(){
  pinMode(redPin, OUTPUT);
  pinMode(greenPin, OUTPUT);
  pinMode(bluePin, OUTPUT);

}

void loop(){
  for(i=0;i<=2;i++)
  {
    for(j=0;j<=255;j++)
    {
       analogWrite(color[i],j);
       delay(5);
    }
  }
  delay(1000);
  analogWrite(redPin, 0);
  analogWrite(bluePin, 0);
  analogWrite(greenPin, 0);

}

Answer 1

The problem has been solved (I think) by connecting the GND for the IC and the (-) side of the adapter to the GND of the Arduino.

Answer 2

Since it works fine then powered from Arduino, I guess this is hardware, not software problem. Arduino port providing around 40mA, while each colour of Dioder sync around 140mA. Do you use any amplification, like FET or ULN2003? Can you post your schematic?