Quarter the potatoes and place in a large pot. Cover with water and bring to a boil over medium high heat. Boil for 15-20 minutes until a fork pierces the potato easily. Drain and let cool.
In a large bowl, combine the mayonnaise, salt, turmeric and mustard powder. Add the chopped onion and the olives. Peel the potatoes and then cut them into small chunks. Add to the bowl with everything else. Stir and refrigerate.