You are right, it's not very easy to distinguish it. But I think there are some small differences between nickel and steel. Nickel is a bit more yellow and steel is more grey, steel is harder so often the relief on the coin is lower. Nickel also has a different lustre, especially when it is worn.
I'm not orange and also in other things I'm not a Donald at all. DonChori like Don Felipe or Doña María, por favor.