First, Advent is not six weeks. It begins on the fourth Sunday before Christmas, and ends (one would think 'ipso facto') on Christmas. Christmas is it's own season with it's own liturgical colour (White), and lasts (as the song says) 12 days. It is followed by Epiphany, whose length is determined by when Lent begins: Epiphany ends on Ash Wednesday.
Second, the colour (singular) for Advent is usually Blue nowadays (representing anticipation and hope); but there are some who still practice it as a 'mini-Lent', and therefore use Purple (representing penitence). For further explanation, see 'Lent' below.
Third, I feel it is worth mentioning that Lent begins on Ash Wednesday, hence 'Mardi Gras' (fat Tuesday), 'Shrove Tuesday', and 'Pancake Tuesday' all represent a time of indulgence and festivities before the long period of fasting and repentence (and a chance to empty your larder of anything that will go rotten before the spring).
Lent is actually 46 days long, because the actual '40 days' do not include the 6 Sundays which fall in Lent (they are considered 'Feast days' - days when the fasting does not apply).
Fourth, while the traditional colour for Lent is Purple (the colour of Royalty and of penitence), many churches chose to use Blue instead. They have been turned off by the 'fire and brimstone' over-focusing on our sinfulness and unworthiness connected with Purple (our human side), and chose instead to focus on our worthiness and anticipation of forgiveness (our partaking in the divine).
Personally, I believe that a time of penitence and introspection is more necessary now than ever, but this is my opinion and separate from relating the facts of liturgical colours.
Fifth, Advent and Lent are a single colour, either Blue or Purple. They are not that colour AND White.
White is it's own liturgical colour, used at Christmas, Easter, weddings, baptisms, and sometimes funerals (instead of Purple, for the same reason as above). It is also used on some Feast days paticularly associated with the power of Christ (i.e. the Conversion of St. Paul, The Annunciation of the Lord, the Confession of St. Peter, etc...).
Sixth, Red is used during Holy Week, because it is associated with the 'passion of Christ'(the Sunday of the Passion is now often held in the same service as Palm Sunday).
Red is also used on Saint's days (i.e. St. Andrew, St. Paul, etc...), and Feast days (Holy Cross Day, the Holy Innocents, etc...).
As you clearly stated in your lesson, Green is everything else.
I realise that the 'Feast days' and 'Saints days' are not applicable to most 'non-Catholic' denominations (i.e. Protestant); but there are many Lutherans, Anglicans/Episcopalians, Roman Catholics, and perhaps a few Orthodox who use this site and it's information. It is for them that I share this, and to clarify the few 'mistakes' that I found.
Cheers
St. Catharine
Anglican (and future theologian)
