I would like to white wash my woodeck with a turquoise color.

Yes you can do that. Wood stains can be mixed in any color. If you have an oil stain that can be tinted as well.

If you do want a white washed look use an exterior paint and paint and blend just like any other surface. It will add a nice character to your deck.

Well I think "white wash" means white. But if you are asking if you can give a color wash of turquoise to your woodwork, yes you can. If it doesn't look right to you you can re-paint. So I would do just four or five feet and live with it for a while.

If your deck gets a lot of usage and weather, you might want to think more of a stain than a paint.

I've added a link below so you can get some ideas of the coverage/look you are wanting.

https://www.pinterest.com/tamycavan/turquoise-wood-stain-paint/?lp=true

when you do it will need a evostic water based sealer applied on top to stop it washing away eric