White Chocolate M&M's was a Flavor M&M's (not confused to the Easter one) was a limited version for Australia only in 2004. It was then put in a statement for revival from Mars on this message:
“M&M’S White Chocolate will hit shelves at select food, mass, convenience and drug stores nationwide starting in May 2017 in Singles (1.5 ounces) packs that feature the brand’s iconic colorful candy shells.”