treatment for Ironbark and Oregon outdoors

Hi all

I am about to build a carport using Ironbark poles/logs and Oregon for the beams and rafters. I'm looking for suggestions of how I can treat it so that the timbers maintain their natural colours and don't turn gray with age.

A few months ago an architect told me about the Ultralast product range. I have been looking at possibly using Ultra-Varnish. Supposedly you don't need to recoat it for years. Has anybody used this and how did they find it?

I was looking at the forums last week and there was some talk of people using motor oil on workbench tops. Does this keep the original colour and would it be any good outside in the weather?

If neither of these ideas is any good then any advice on what to use would be appreciated. Of course the preference is not to have to recoat too often.