Otherwise known as bleaching. Is this something any of you DiSers have done before?

I'm thinking of bleaching my hair but apparently it's irreversible. Is this true? I wanna dye it blonde so I can then dye it bright orange (I dye it orange with my natural dark brown hair but it never comes out bright enough/doesn't last long). But I'm not sure I'd never want to be able to restore my natural hair colour ever again.

Have any of you DiSers done it and did you regret it?