Well, the shrapnel would give impulse to the combustion fumes released in the detonation, and that momentum would carry outwards until the gas dissolves into the space.
It would look much similar to fireworks, flash of light and an expanding and rapidly dissipating cloud of combustion gas, which has "spikes" in it caused by the shrapnel.
It wouldn't really look like the fireballs we have now. If any of you have seen artillery or mortar strikes, you know it doesn't look like fireballs fram movies either... There's a small flash of light, but it's almost completely concealed by cloud of smoke and dust... and the dirt and shrapnel flies almost directly away from the explosion center, causing spikes much similar to what I described. Like in this:
Not the best example, but good enough for it's purpose. In space, obviously there's no dirt to fly around, but the smoke would be the most visible component of the explosion, and of course the initial flash.