Here ya go! It's tips about cuts as well, but rule #6 explains how a darker root gives your hair 'depth.'
I went an all over bright blond, blunt bob around this time last year and it was really cute but I tired of it pretty quickly. Had some high and lowlights put through next to bring back a more natural shade, kept the blunt bob and really loved it. I could PM you the difference if you're keen. But definitely no harm in trying it out and if you decide you're not keen just have it broken up next time.