@NatashaDancing
The photos objection really puzzles me. The OP is the guest of her boyfriend who is a friend of the bride.
There will be 200 guests there. There's every possiblity the OP won't even be in a photo or she'll be part of a group or behind someone else.
If there are group photos, as there often are, where all the guests are included, I personally wouldn't want to stand out in a white dress as a guest at a wedding.
As a bride i wouldn't be arsed, it wouldn't cross my mind. Unless someone turned up in an actual bridal gown.
As a guest I would be mindful of wearing something that is mostly white, and add colourful accessories to tone down the white.
That's all.