You cannot tell everything by the "color" of the gears.
Birdman is correct , if they are brown or even "goldish" colored then yes they are cast gears.
However, there are alot of "silver" looking cast gears as well.
The steel gears you can EASILY see machine marks in them.
If you look at a known cast gear, and hold a steel gear up to it you will see the difference IMMEDIATELY.
If you are holding the two gears side by side, and your still unsure about it, most likely not a steel gear.
The difference really is that easy to tell.