Yes absolutely. You can use a mixture of greens and make "saag aloo". Indian palak aloo is just made with spinach & potatoes, however, for saag (a combination of various types of greens), make sure to keep cooking times of different greens in mind. For example if you are using kale (that takes long to cook), either used blanched kale or baby kale when combining with fresh spinach(that cooks way faster).