Interesting about the different color for German. The sisters at our nearby convent always sing Stille Nacht (Silent Night) in German at Midnight Mass it is quite moving. I will have to look at their Advent Wreath more closely this year to see which they use!
I saw a photo of Pope Benedict with his own Advent wreath - it had red candles.
In Spain we use always a white candle, a red candle, a green candle and a purple candle.