While I can't speak for the entire nation of India (I moved to the US as a child), I clearly recall being taught VIBGYOR by my father, and then later learned it

While I can't speak for the entire nation of India (I moved to the US as a child), I clearly recall being taught VIBGYOR by my father, and then later learned it as ROY-G-BIV in school in the US. So I'd bet it is a cultural thing.