The better the metal prep/polish, the better the final product. Blue Wonder works pretty well...more a black than a blue, which is OK as that more closely matches factory hot-blues (whihc are pretty close to black). Decently long wearing.
Brownel's Oxpho-Blue is another good product...easier to use, long wearing, and about as simple to apply as possible. Will be more of a blue, which won't match factory blue-black all that well, but it's so easy to apply and last so well, it tends to be my favorite touch-up or small parts blue. Prefer the "creme" as it is easier to apply.