Ask her out.
But dont be surprised, after all this advice, if she declines...truth is, you were already given the giant green light, but didnt proceed! Very often such signals have an insanely short shelf life...or none at all. This due to women's expectations that you can read her most obvious social signals, and are assertive and risk taking enough to follow through. But ask her out even if not a sure thing.
I'd not ask her "uh...hey so uh, wanna go out?". I'd resurect the joking conversation from the other day, keep it the joke, then gently suggest you meet for a drink after work, after all she's "blonde and from____, my perfect dating type!" Or some variation of that...
Oh, the short shelf-life I've experienced several times...gotta be quick and play their game, when they invite you to play, or they go home without you!
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