The 20feet of CAT5 cable for the PWM would worry me a bit was well. I would expect some signal degradation particularly if the PWM is running at higher fequencies.

The human eye is more sensitive to green light, so green LED usually appear brighter than the red, or the blue.
This article may also of interest if brightness perception is an issue:

https://ledshield.wordpress.com/2012/11/13/led-brightness-to-your-eye-gamma-correction-no/

If you scroll down the page on dsscircuits.com you'll find a pretty detailed timing comparison between the I2C and wire library ;-)
That should explain any performance differences.

Perhaps you want to post your problems on the forum dedicated to the teensy boards:

http://forum.pjrc.com/forum.php

I read through your initial post again.
If you are interested in a real WiFi solution I would currently not recommend any WiFi shield and suggest an alternate solution using a " standard" Ethenet shield connected via short Ethernet Cable to a little pocket router. That way you will not have to rewrite code but still are able to use a WiFi connection:

http://arduino.cc/forum/index.php/topic,149865.0.html

PaulS....I like your humor.....most of the time. This was the second time today that my kids asked me what I was laughing about when reading forum posts. That made an otherwise crappy day much better.

http://diysandbox.com/our-products/platinum-arduino-mini-with-wifi

Here you go.

Just to summarize a few things

1. Using a little ( half the footprint of an iPhone 4 and about twice as thick)  TP-Link router will enable you to connect directly with the iPhone to the router/Arduino because that little router comes configured as an Access Point out of the box. You plug it in, it shows up in the WiFi connections in your iPhone and you're in business.

2. The TP-link TL WR703N is available through eBay ($20+) and I've had no one preventing me using it in my projects due to a missing FTZ certification YMMV. The user interface is in Chinese. Google translate helped me.

3. If you have a home router you can have the TP-Link also connect to your home router and access the Arduino wirelessly through your iPhone<-->home router <-->Tp-Link<-->Ethernet <-->Arduino. That is an interesting setup if your project is located somewhere inaccessible for a cabled Ethernet connection. I use this set-up in my projects ( trippylighting.com).

4. You can also omit the Ethernet card and connect the TP-Link WR703N through its USB port directly to the Arduino, but it requires you to flash an OpenWRT Linux based router software on it to begin with. I have no handson experimece with this, but I believe that this will not work with Ardumote as Ardumote usesthe UDP protocol for communication and I am not aware of an Arduino library that supports UDP over USB. If that ever interests you, it is not required to purchase a preflashed one of eBay, unless The fine folks at the OpenWRT website are untruthful ;-)

5. The fact that Ardumote ( and TouchOSC, which I am using in my projects) work through the UDP protocol is also the reason why I would be careful with using a Bluetooth module. Getting that to work will almost always require you to socket programming and worse ;-)

6 Using Ardumote with the Ethernet shield directly or through the TP-Link Wr703n has worked flawlessly in my projects but I have since migrated to TouchOSC.

This should fit the bill.

No. You just need to carefully read what's written before even attempting to touch the keyboard. The Xbee is N O T a WiFi solution. It's adheres to a different wireless standard but NOT WiFi. E.g. You cannot connect directly to it from an iPhone or Android phone or connect it to your internet router.

Perhaps because you cannot connect an iPhone to an Ethernet cable, unless ther is some form of an adapter that I am not aware of.

I agree with Pauls, however, that using a WiFi shield is not nearly as trouble free as an Ethenet shield.
However there is a solution that is almost as trouble free alas at a little added expense.
You can connect a little pocket router Tp- Link WR703n etc, to the Ethenet shield and voila, you're in WiFi business.

The Wireless SD shield is not a WiFi shield. WiFi is not the same as Wireless.
The Ardino Wirless SD shield needs to be equipped with an XBee wireless module. You did not mention what module is installed only the shield.
Whatever you do have installed however I'd believe makes no difference. The library you are referencing is meant for the specific wifi hardware on the Arduino WiFi shield and will not work with the Wireless SD shield.

Please put your code in code tags when posting!

To answer one of your question, the smaller cap needs to sit closer to the radio. These capacitors are needed to filter out noise on the power supply side and have not much to do with the 2.4GHz side as Docedison mentioned.

That does not need to be on a spec sheet as adding decoupling caps is very common practice ( as Docedison also mentioned) and one of the very first things I learned ( the hard way :-) when I started with electronics 20+ years ago. That is not specific to these transceivers!

When asking for help, please consider to provide as much information as you can with the minimum being:

- Links to the exact hardware specs that you are using
- the code/ sketch that you intend on running on your Arduino

And please put the code in code tags so its actually readable. Without that minimum we cannot really provide much help!

It would probably help you if you scan through the many posts in the LED section of this forum.
The first thing you'll learn is that running LEDs in a parallel configuration is not good practice as LEDs are constant current devices. that also means that you need tight current control, and not voltage control.

Automotive applications can be challenging as the voltage/and current levels are quite varying and most automotive LED chips are buck/boost LED drivers for that very reason.  Also, you may want to check what laws apply in your country of residence. You may get away with tinkering around with these things in the USA, however, in Germany the police woud remove you vehicle from the streets immediately and you'd be heavily fined for tinkering around with elements on tha car that are considered safety relevant.

I am not suggesting not do it, however, I think for a first Arduino project you may have bitten off a little more that you can chew. Perhaps you want to start with something less complex that will have a better chance of success and keeping you motivated for the more challenging project you have in mind.

If you're familiar with Eclipse your can try to use the Arduino Eclipse plugin:

http://eclipse.baeyens.it/

There a a few lengthy threads about it here on the forum. I've started using a beta version with my Teensy++2 board and it works nicely for me.