I don't know where that perception came from. I don't make a big deal out of every holiday, but we do acknowledge most holidays even as we go about our normal routines, and try to learn something about their origins, purpose, etc. The idea that MLKJr. Day is only for black people didn't come from me. But I will make darn sure that we talk about it today.
Here are a few resources that you can use in your homeschool, or just to learn for learning's sake.
short biography of MLKJr.
Videos on History.com
Printable activities for elementary & middle school students
Numerous links from Easy Fun School
Martin Luther King Jr. Lapbook
Famous MLKJr. quotes: cursive copywork pages
Martin Luther King Jr. quotes
"I Have a Dream" speech