The color mauve isn't a sin.
The Bible doesn't speak of the color mauve as "working that which is unseemly" or "forsaking the natural use." (Romans Ch 1)
Impressionable young people who see the color mauve may very well walk around and say, "Hey, evidently there is nothing wrong with mauve, because they have painted their house mauve and my parents and society say it is okay, so it must be okay. Or they don't speak out against it, and if it were wrong they would speak out against it."
And yes, we need to speak out against heterosexual fornication as well. Not speaking out against it has resulted in the shape of families (or lack of families) today; young people seem to believe that fornication is no big thing anymore. They don't realize that it impacts their entire life, many times in ways they don't know.
For instance, many times a person who has been in this sin, when married, struggles to attain a level of intimacy because they have learned to hold back part of themselves. It was the only way to protect themselves when they were sinning. Now they have a stronghold in that area, and it is a problem for them and their spouse.
Not only that, but the Bible clearly says that we are not to be deceived, and then lists those who will not inherit the Kingdom of GOD. Fornicators are among that list.
However, heterosexual desire is not against nature, the Bible clearly says that homosexual desire is. God will bless heterosexual desire as long as it is within marriage; saved couples can and should ask GOD to anoint them to meet the other person's needs so they can be a blessing to their spouse.
BBoy