My DH and my DS (4 years old) both want blue magic bands. Will it be a big hassle for them to have the same color, or really not a big deal since names will be on it?
My daughter and I both had pink ones and it worked out well. I bought little bows to put on each one to differentiate them. There's accessories for Magic Bands in Disney. I'd just buy something small to add to each one to make them unique if it gets confusing.
Also, at the age of 4, your DS will probably be more comfortable wearing his band if the middle section gets pulled out from the outer section (which is designed to happen to make the bands more adjustable in nature). Then your DH's will be blue with a grey accent trim around it while DS's band will be solid blue.