[Hutch]

Either post a pic of what you think is original color or give us some kind of idea what it looks like.
If you have the option list inside the glove box as 68 Suburban stated check there first.
Does the truck have the color separator chrome trim at the back of the cab?
If so then it would probably been two tone.
Some trucks had a copy of the original build sheet stuck inside the seat. I have never found one but other board members have.
That of course depending if the seat in your truck is original.

Supply some more information (year, model, options, fleet, step, trim) and post it here and I am sure that someone can supply you with the correct color code for your truck.

Have Fun