I know that David Wise and his contributions to TMNT history has been a hot topic of debate on another thread, but I figured I'd at least post this update here for posterity's sake.
On his FB account this week, Wise posted a screencap of the Lupin III episode in which Fujiko is wearing the yellow jumpsuit/white boots which came to be associated with April O'Neil in the old show:
I'm not a Lupin fan, so I have no idea which episode that was, but that is the first visual evidence I've seen on the specific look being copied. The middle picture of the statue is the outfit that Fujiko wore in
Castle of Caligostro in which she did pose as a news reporter.