What is the colour of iron after rusting?

Answer 1

As for the most of rough surfaces of cast iron, the color is grey. Such as normal grey cast iron and ductile iron.

The ductile iron will be more white than grey cast iron.

There are few types of vermicular cast iron, which are black.

The white cast iron will show white color.

So, cast iron has different color, such as grey, black, white according to different types.

However, most of cast iron castings need surface coating, such as painting or electroplate, so they will show different colors than their own.

Answer 2

The color is turned to red (from iron oxide and hydroxide).