I was hypothesizing elsewhere that it is orange because it is still not fully flight certified (we use the word "qualified").
The USAF paints items that are on an aircraft that have not met all of their environmental specification requirements orange to easily distinguish them from fully qualified items.
I've had to deal with orange bomb racks, orange bomb bay door control avionics, orange weapon release hardware, all kinds of stuff, so an orange bomb is reasonable, I suppose.