oops, the link did not work for me. However, I will answer your question:
It is NEVER good etiquette to wear white to a wedding. You see, when a guest scans the room for the lady in white (or cream) they are looking for the bride. If a guest is wearing that color, then their eyes stop looking and they realize that that woman in white is not the bride. All the while that woman in white is stealing attention from the bride. Not saying you are doing that, mind you, but that is exactly what the guests will think. So, refrain from wearing white and select another dress because this wedding is nothing about you. Sitting at the head table is also another BIG reason not to wear white.
Find another dress.