You can get solid color stains in a number of flat colors. Wait until the wood is definitely dry. Wash with deck cleaner/brightener for good adhesion. Apply stain. Cleaner & stain generally available anywhere selling paint.

Thanks David! -Steve

There are coatings made for use on CCA (chromated copper arsenate)lumber right away, but if you want to use regular paint you have to allow time for the solvents in the treatment to evaporate, or they will come through the paint and degrade it. Be careful around this lumber, the chemicals are meant as poisons for various microbes and insects etc.