Even added a simple decking oil can transform the colour of the area to looking brand new, a colour which might look nice is a sage green, especially if you decide to get white and green plants!

I would always suggest leaving wood to weather naturally. When it reaches a pale grey colour it is strong and should last for years. Remember, staining, oiling etc wooden structures means that you will need to re-apply products every couple of years. Also, if you plan to cover the pergola then why stain it at all? As far as plants are concerned you could plant evergreen clematis armandii with white flowers, or Clematis urophylla 'Winter Beauty' for white flowers during the winter, even deciduous clematis montana. Clematis grow quickly and will soon cover the pergola. You could also plant evergreen trachelospermum jasminoides for scent or jasminum officinale or wonderful wisteria floribunda alba. As for shrubs you could add cornus kousa, climbing rose 'Iceberg, or rose madame Alfred carriere, perhaps some grasses like pennisetum and calamagrostis - there are lots of white flowering plants. It all depends upon the aspect of the garden and whether or not you plan to plant in pots or in the ground, and how hands on a gardener you want to be. You need to think about framing the view, rather than blocking it entirely. I hope this helps and I wish you all the best. Try, experiment and enjoy. There may be casualties along the way, but that's how we all learn to garden.