Looks like a Stomatella varia to me, rather than an abalone. All abalone shells have holes in a line in them. That's one easy way to find out for sure.
Well abalones (all in the genus Haliotis) get huge. They would move around rocks and generally make a mess of your reef tank. But otherwise they are harmless herbivores.
And yes, S. varia can have that irridescent shell. The varia refers to the many different color morphs of the species IIRC. They are brown, white, grey, yellow, etc.