I thought it was inadvisable only for the bride herself, not guests.
I found this old rhyme, and another theory about green:
Married in White, you have chosen right,
Married in Blue, your love will always be true,
Married in Pearl, you will live in a whirl,
Married in Brown, you will live in town,
Married in Red, you will wish yourself dead,
Married in Yellow, ashamed of your fellow,
Married in Green, ashamed to be seen,
Married in Pink, your spirit will sink,
Married in Grey, you will go far away,
Married in Black, you will wish yourself back.
A green dress is thought to be unlucky unless the bride is Irish. The old expression that a woman has a 'green gown' was used to imply promiscuity, the green staining being due to rolling in grassy fields.