Since when is a blue or pink cake offensive?

Amber
Ok, so I made the announcement today to my staff about the upcoming arrival. One coworker said "ohhh we should have a reveal party with cake" another flipped out saying a reveal party is offensive to the LGBTQ community and assigning a baby's gender and celebrating it is a big issue. 
So this is my question... this is my 3rd child... so since when is cake and celebrating the child regardless of the gender offensive?