Never used a CMU Cam but....if you're trying to do the image processing on the arduino board (or most small controller chips) then you have a challenge. The camera may be able to detect a yellow blob - but not necessarily the direction it is pointing in - it will probably just give you a list of rectangles that mainly contain a yellowish colour. Obviously an arrow changes shape depending on how far away it is and the angle of your camera to the ground.
Check the code for the board to see what it is capable of.
My experience is that once you've got a rectangle then reading individual pixels in the rectangle is very slow and would be clobbered by the next incoming frame.
Better alternative may be to look at the 'yellow' rectangles and just ASSUME that one leads to the next - but your 2D rectangle view of the world may not agree with the 3D world but should be okay if the arrows are of the same size (ie you could look at the rectangle area (wxh) to guess how far away it is).