Easiest form of Color sensing?

[Asymphonic]

We're constructing a robot whose basic mechanism will be lifting a box (about 18x18x18), detecting its color (either red, blue or green), then tracking a line to get to a three-path junction, where it'll read the color off a pad on the floor (again, either red, blue or green), and then follow the track to place that box in a slot of the pad's detected color.

There are basically two things we need to detect.
1. The color of the box
2. The color of the pad.

The box will likely be made of wood and spray painted.

What is the easiest and most accurate way of doing this?

Also, is it better to use IR emitter/detectors or simple color sensors?

[Razor Concepts]

Here is a cheap color sensor:
http://www.sparkfun.com/commerce/product_info.php?products_id=8663

Another alternative is to use 3 different colored LEDs configured as light sensors. For example, a red led would give a big signal in front of a red object, and the green/blue LEDs would give smaller signals.

[Redcap]

I've recently been researching such things myself. If you choose the DIY option, this link may help.

(A schematic of a complete working implementation is shown on the 2nd page)