Normally I would have said leave the wood unstained and just clear coated but the gray flooring will not work well with thta . Waht was the reason for the gray floor ? I normally like porch or deck floor to look as close as possible to the interior flooring and that would have worked with a clearcoat pine. Now IMO a whitewash for the pine .

I'd do a solid white stain, or paint, even a very light blue (BM Iceberg) the pine will golden over time, and certainly the knots will bleed through anything you do.

it really depends on how dark you want the room to be.

I always prefer outdoor spaces have light ceilings for a fresh outdoor feel.

The darker the stain color the less light reflectance you will have in the interior of your home.

I think blue paint would look good with the gray floor. I would do a natural looking color for the deck or a light gray.