Does your couple like Italian touch?
There is this Pastamania, some of its outlet e.g. in Northpoint Yishun, are nicely decorated.
They may have Vespa in display. 313 at Sommerset also has a vespa, I could not remember the restaurant name, but I think you should check with them, e.g. if you order food, will you be allowed to take photos. The next door Forever 21 may have retro accessories to suit your theme.
Color range: red, green, white (just like the Italian flag).
You can ask them to wear old days large plastic sunglasses.
Wear stripes-pattern dress / shirt.
Tie a hair-band, big earrings.