I have been doing something similar over the last year for my motorcycle.http://arduino.cc/forum/index.php/topic,8381.0.html
I started it last spring. But then the weather got warm and I would rather spend my time on the motorcycle
I was also delayed because customs held my bliptronic leds for a couple of months.
I have gone through 4 different designs because I keep adding features. I'll give you a quick summary of what I have done and why.
My original plan was to make some accent LEDs that I can control and make custom effects. I wanted to control them remotely and I wanted the ability to add effects later on easily. I found a 4 button remote. I will have a microsd card holding animation information. Some animations have to be programmed - anything that has random numbers. The microsd card will will contain frame based effects.
I started with a tlc5947 led driver chip as that is the first thing I came across in my research. The first video in that post is me making sure I can control the chip. Those LEDs are once I had around and they are a pain to work with. I found a led strip on ebay that takes 12v (perfect for a car or bike) that could be cut and used like individual LEDs with the tlc chip. I got that all working fine.
Then I saw the Bliptronic pixel LEDs. I really liked that idea over the tlc5947 because it would be a lot less wiring. In a car, you can hide wires in door panels and such. On a motorcycle, not so much. So I picked up some of those. They work great but I ran into a problem. Since you have to manually control the PWM cycle that takes up processing power. Some of my more complex animations affected that causing the LEDs to flicker.
Luckily, the next week Sparkfun came out with their addressable LED strip. The chip they use has it's own PWM cycle. That is a super easy LED strip to work with.
Right now I am in the process of converting the code to a Netduino Plus. The Netduino Plus has built in ethernet and microsd. This gives me more I/O pins for future expansion. Plus the fact that I can do line by line debugging makes it easy to code. I am going to use a small wifi router connected to the ethernet port and control it with my ipod touch instead of the remote.
I am still going to finish the project with the Arduino as my sister wants the basic setup on her bike. One idea for future expansion is to use xbee or some other wireless communication between my bike and my sister's bike to have in sync animations when our bikes are next ot each other.
When I ordered the Bliptronic LEDs I also grabbed the audio analyzer shield. I will add some modes where the LEDs are controlled by music.
Finally, FYI, the US government definition of amber warning lights is actually orange. 100% red, 50% green. I was going to use my LEDs as running lights (anything to make a motorcycle more visible) but running lights are only legal on trucks and emergency vehicles.