The pearl has often been taken as a symbol of purity and perfection in love as they are amongst the few spherical things that it is possible to find in nature. They are a rare and precious jewel, just as pure and perfect love is. They have also been called a symbol of patience and determination as it takes many years for a pearl to form within an oyster and, as many people know, they form from a grain of sand. In other words, they form from a substance that the oyster reacts to like an irritant. This gives a great deal of symbolism to the pearl as a gift for the 30th anniversary.
For those amongst us who are religious the pearl also has a great deal of significant in this regard. In the New Testament the pearl is often used as a symbol of the kingdom of heaven and a good marriage has often been called a foretaste of heaven on earth. In Islam the connotation is similar with those who are in the afterlife being described as adorned with pearls in the Qur'an.
The reason why this anniversary is symbolised by the colour green has been lost in the mists of time although it is well worth remembering that green is usually used as symbolic of life, birth and rebirth. We use green to celebrate springtime at Easter but we also use it to celebrate Christmas in the form of the Christmas tree, even though much natural life is hibernating at this time of year. The colour green may be there to remind you that the spirit of your youth still lives in your marriage, 30 years on. Many couples celebrating their 30th anniversary will be just entering their 50's and some may be struggling to acclimatise to this different stage in their lives. The colour green may be there to remind them of how much is the same in winter as in springtime.
The flower associated with this anniversary is the lily. Many people associate the lily particularly with the white lily which can, again, be seen as a symbol of purity and perfection. Lilies and pearls definitely go together. However, if you would prefer it is possible to get lilies in all different sorts of colours to suit whatever colour scheme you would prefer and to match whatever decorations you may be hanging.