I can't wait to see photos !! Sounds like my kinda thing . White came to mind first for me too . Huldine has a pretty reverse that shows plum colored.

But maybe something like ville de Lyon would look really pretty too ! Or Guernsey cream is a hint of yellow . Sounds like a great project no matter what you choose . Maybe something will jump out at you at a nursery

I think purple or pink would be tough with the combo of orange, turquoise, and cobalt. You could go for white, or one of the really deep purple-red/maroon such as Romantika; or one that is mostly white with pale color like Ice Blue or Vancouver Fragrant Star; or one that mostly white or light but with a colored edge or reverse such as Omoshiro.

Here is a pic of the bottle tree from today

A Clematis is going to need something like wire mesh to attach to, they won't just climb a 4 x 4. Huldine will get waaaaay too big.

Not too much yellow or orange, so go for whatever color you'd like, though I am not sure I'd like lavender with the turquoise. Be sure to research the size since 6' (is that above ground or total height?) is relatively short for clematis.

I'd start the nails/pegs within a foot or so of the ground and leave some without bottles - the clematis can cling to them but the bottles may make it difficult for the plant to grab them. (or loosely fitted mesh as BorS888 suggested.) Clematis climb by twining their leaf stems/petioles, so need something pencil thickness or thinner to wind around for climbing.

I am leaning towards something raspberry pink be I like turquoise and raspberry. Will definitely surround the post with wire or guide nails to allow for an easier climb. Thanks all! Now to find one I like that is tall enough to climb this year.