On trick is to wash your hair in hot water with a volumizing shampoo like Kenra Volumizing Shampoo or similar. You can find it really inexpensively on Amazon.com or EBay. No need to pay salon or even boutique prices.
Apply the shampoo full strength and suds up. Leave the shampoo on for a few minutes. Rinse well and then apply a volumizing rinse out conditioner. Rinse and then rinish with a cool/cold water rinse.
Use an volumizing leave in conditioner and then blow dry hair.
The combination of the volumizing shampoo, conditioner and styling products will blow open the cuticle and help to dilute the color a bit. Also heat will instantly fade color.
If you really want to lighten it up, apply a hot oil treatment before you wash with extra virgin olive oil (EVOO). Olive oil is famous for lightening hair.
Hot irons will also help to diffuse color due to the heat on the strands.