Step 3: Electronics Pt. 3: LED lighting
I would reccomend going to eBay and buying an LED assortment. Whenever you need a color, you'll have it on hand. I purchased 7 colors of LEDs, 15 LEDs for each color, for about 6 dollars shipped.
If you want to drive more than one LED on the Arduino, you will need to use a transistor (basic schematic shown in pictures).
The LEDs are connected to the digital ports on the Roboduino, and used the digitalWrite command to turn the LEDs on and off.