Back in 1966, you could be "Sew in with the crowd", if you made one of these dresses for yourself!
A "see-through chiffon overslip" with a slip dress underneath.
Or wear the slip dress alone for "another swinging outfit".
done up all in white here in this advertisement for McCall's out of a 1966 Seventeen Magazine:
But I think it looks stunning in black!
See the depiction here on the pattern front:
available on Etsy from Deja Vu Patterns, it really IS pretty:
Or whatever type of parties people are having nowadays.