Weathering Wood Decks

For weathering wooden decks I use a gray wash.  When exposed to sunlight and weather, woods that start out shades of light brown soon turn to gray.  I just use a very thinned medium gray paint as a wash.

Similar, I have used a semi transparent stain, I think Minwax. Colors are usually called something like Nantucket, or Driftwood etc.

Do I need to seal it first? if so, can I use Tamiya's flat coat in a rattle can?

If "Gray" is what you are looking for, I use Micro-Mark's "Age-It Easy". Just brush it on unsealed wood. They also have a brown, but, I have not used nor seen what the results are.