Audiosurf D consists of two different modes: normal mode and D-Risk Mode

Normal Mode: When you're moving around like normal. Hit the blocks to raise your D-Mode multiplier. Greys reset your multiplier. However during normal mode your points don't get affected by the multiplier.

D-Risk Mode: Press Mouse1 to enter D-Risk Mode, an indicator will pop up under your ship as a visual cue. When in D-Risk Mode you can't raise your multiplier, but any board clear points will be affected by the multiplier. Greys still reset the multiplier. It is possible to get no points from a board clear if your multiplier is zero, so be careful!

Note: board is erased when entering D-Risk Mode.

Have fun!