RGB Scratcher

Dimmering full color lamp with  pencil scratches.
If you do a mistake on your note, you erase the mistake with scratching with a pencil. I am intersted in this interaction and want controll light in same way.
The lamp has 3 control point each for red, green, blue light. When you scratch with pencil then the light will be cotrolled.
I used a LEGO block which are my origin of creation. It is also nice material for rapidprototyping.