.White sage is probably the most common and popular herb for smudging. It is associated with purity and has a strong and heavy presence. It's definitely useful for when you need a major space cleansing.  The 7 Colors represent the 7 Chakra system
 
Red for Root
Orange for Sacral 
Yellow for Solar Plexus
Green for Heart
Turquoise for Throat 
Blue/Indigo for Third Eye
Purple for Crown
 
When burning set your intentions and light it up.