In a world where we have already been preconditioned to certain design patterns, the blue button is clearly the more prominent and will subconsciously be considered the "default" option.

Worse than that - I expect most technology-illiterate users won't realise the "Not now" text is a button at all.

(Its grey-on-white designed to look identical to the copy text above the button. The only difference is placement, and a small difference in font size.)