Red - Rune wards
Yellow - Ubercliffs
Pink - Lane/aggressive/defensive/ wards
Green - Jungle wards
Blue - Push wards
White - Very situational
Purple lines - Blocks the pointed neutral camp from spawning
Read full article here: http://www.team-dignitas.net/articles/blogs/dota/1092/dota-2-ultimate-guide-to-warding/