I have been working on cards for the conlang card exchange, and the greeting I have settled on is Pa imev yevam, vekum, wa imlam dez gyet Shuf-shevélat! This builds on the previously formulated "pa imev...dez" ("I wish for your...") formula created for birthday greetings.
I think I might keep this as a set greeting/blessing/cursing formula and work on some grammar to handle more complex thoughts about what one person wants another person to be/do/whatever.
Shuf-shevél or Shufshevél is the Nevashi fish celebration, which is exactly that the name means. Once mainly a fishing and seafaring island culture, fish represent prosperity and fertility for the Nevashi. The symbolism remains, even for mainland Nevashi, who are mainly farmers, traders, and merchants, far removed from their roots. Blue, green, and gold are the traditional colors of this holiday, carrying much the same significance as the fish.
On Nevash, the custom is for each household to buy or make an unfired clay pot in the shape of the fish. Small token offerings, such as coins or bits of food, are placed in the mouth of the pot. There is a procession down to waterside in the morning of the first day of the celebration, where the pots are tossed into the water. Those inland on the island may go to the nearest river or lake instead. With that out of the way, the real festivities begin-- there's a lot of feasting, drinking, singing, and gift giving. Fish-shaped jewelry is a popular gift, widely believed to bring good luck.
Originally, the festival was held after the trees had lost their leaves but before freezing temperatures set in, on whatever day the local temple declared auspicious. It has become loosely associated with the winter solstice due to contact with cultures that celebrate that occasion, and the increasing centralization of religious and civil authority has led to more and more towns and villages holding their festival on the same day as the capital city. The length of the festival is determined by either the local temple or the temple in the capital city, as determined by the same sort of augury that sets the date of the start of the celebration.
Mainland Nevashi, removed from the island culture, still celebrate the festival, but with customs that have evolved to fit their circumstances. It is still a celebration with a lot of feasting, drinking, and gift-giving, with slightly different details. Those communities in close contact with solstice celebrating cultures may have both night or sun themes, in addition to the traditional fish motif, but they still call it Shuf-shevél.
Almost every mainland family owns a fish-shaped vase, which tends to be very ornately decorated in the colors of the holiday. A fish festival vase is often the gift of choice to a newly married couple from the bride's parents-- either an heirloom or a newly purchased one. Wishes are written on pieces of paper and put into the vase on the first day of the festival, which tends to run a full 5 days on the mainland. On the last day of the festival, the wishes are thrown into a fire unread-- it's considered very bad luck to read anything that goes into the vase.
The second day usually involves a blessing of tools of work, in order to bring prosperity. The remaining days each have a different theme, such as "gratitude" or "remembering Nevash", etc, varying from community to community. Every day involves parties and feasting, with menus varied to fit the theme of the day. On the last day of the festival, the wishes are thrown into a fire unread-- it's considered very bad luck to read anything that goes into the vase.