Carrie Underwood is flaunting her huge engagement ring on Instagram — and it's all for a good cause!

The American Idol winner showed off her yellow diamond sparkler from husband Mike Fisher — and a very unique purple manicure — to raise awareness for domestic violence after being inspired by fellow country artist Jana Kramer.

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"Hey @kramergirl it took me a couple of days to get my nails done, but I'm happy to join in the #PutTheNailInIt movement to help bring awareness to domestic violence," she captioned the pic. "Thanks for helping so many women by sharing your story."

The social media campaign #PutTheNailInIt was launched by rocker Dave Navarro, who lost his mother to domestic violence.

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"When my mother's life was taken by a violent ex, I was unfortunately a witness to how domestic violence can not only destroy the victim's life, but the lives of friends and family members," Dave said.

Such a great cause! To see more celebrity bling, check out the gallery below.