Hey lets all make up stupid figures and have a bigger argument.
There's no reason to consider blowing out your Arduino trying something as simple as current sensing. I agree that it's not going to be possible to run all the current for the lights through the Arduino and a simple resistor wouldn't be safe. I'm thinking you just use something like this to sense current: http://www.ti.com/product/ina169
...that only happens when you light up the whole string with full brightness white. Colors will always be something less than that.
OK, the chances are that they won't all line up and the built-in decoupling on each LED should help, but half-bright doesn't necessarily mean half-current.
In my experience it's roughly inverse-square - half brightness is about 1/4 current level. These things are ridiculously bright - I can't even look at them at numbers greater than 50/255. A (50,50,50) white is tolerable to look at.
Apparently I have missed a lot in the last little bit. lol. I'm really digging this suggestive input! Thanks guys! With the components in the image I posted of the smaller device they are capable of doing something like what we are talking about...But i'm not sure if it is doing a current draw check. that just seems dangerous to the components. Now, for your guys' mathematical input and some ease, these 5m strands are 30 leds per meter. so not very large of a current draw compared to the 60/m strips. do any of you have the ws2812B strands?
here you go. http://www.aliexpress.com/item/Black-PCB-DC5V-5m-WS2811-built-in-the-5050-RGB-150-LED-digital-strip-light/969633185.html