How to generate moving arrows

You've gotten some great suggestions already. However, I am a particle fanatic and I'd like to say you definitely can use custom shapes for particles, but it depends on which particle effect you're trying to use. ☺

1. Create a comp "Arrow" slightly bigger than your arrow shape size. (if your arrow is 320 pixels wide, set the comp width to 320 + the amount of pixels you want between the arrows in a line). Center your arrow shape in the comp.
2. Drop "Arrow" into a new comp "Arrow Line", 1920 wide and the same height as your Arrow comp, and add the Motion Tile effect.

3. Set the Output Width to the multiple of arrows you want in one line x 100. (So if you want 5 arrows in a line, set it to 500)

4. If you only want a specific number of arrows in 1 line, animate the position of the Arrow layer from left to right.

5. If you want a continous line of arrows, add the Offset effect after the Motion Tile effect, and add 2 keyframes on the X value. Set to 0 on frame 1, and 1920 on the last frame. This will loop your line seamlessly.
6. To color your arrows, add an Adjustment layer with a Gradient Ramp effect. Adjust the start/end points of the ramp to the left and right of your comp.

7. Drop the "Arrow Line" comp in a new full screen "Arrow Array" comp. Duplicate the layer the amount of times you need, and offset each layer in time/position to suit your look.
8. To have the arrows disappear behind an object in your footage, just precompose them together, and add a mask.

Done!

To my eye, this example has 4 rows of arrows doing the same thing, and seemingly symmetrical in terms of left/right. 

That means you actually only need to make one side of one row, then mirror/duplicate and do some time offsetting.

100% agree with Mylenium's suggestion on the gradient - that can be a look you add after or on top of the arrows, instead of coloring them directly. This could be achieved in a couple different ways, including Blending Modes, track mattes, or a small effects stack.

Let us know if you need further guidance!

Could be as simple as a Motion Tile effect combined with a gradient as an overlay for coloring.

Mylenium