In-game reset:
Press Select + Start + R1 + R2 + L1 + L2 during game play.

Hidden shop:
Successfully complete level 6 in story mode, then select the top right corner 
of the screen. 

Ramdom color car. 
When the "Now Loading" screen appear, hold R1+R2+L1+L2 until start. 
You will see your car change color. (Note:Can use in all mode and all car.)