I believe it may refer to this:

"Red wines also vary in color from a light red colour to a deep brownish red and often become lighter with age. One easy way to tell the age of a red wine is by doing a rim test. Tilt the wine towards the rim of the glass and look at the colour of the wine. A younger wine have a purple tint to the wine colour and an older wine will have a more brown shade of red.

http://www.streetdirectory.com/food_editorials/beverages/win...