Untreated Pine Enclosed Porch Finish

Need advise.  I have spent quite a bit of time researching and am having a real hard time making a decision on product.  I am biscuit joining a porch floor in an enclosed back porch/sunroom that is well covered and enclosed with storm windows so it is relatively dry except when windows get left open or things get tracked in from the yard.  I am using UNTREATED 5/4 x 6 pine decking for the floor but am wanting a very dark walnutty finish if I can get it.  I also DO NOT want anything that will peel or need to be stripped when refinished.  Need help with how to prep the pine to take the color and what product to use.  Any ideas?  Anyone done something like this before?