Exterior Window Sill Painting

[Calgon]

I have some aluminium windows that have a wooden frame and window sill on the outside. They are in need of painting. They were previously wood stained.

I will be eventually replacing the windows but for now I have painted the inside of the window frames white and they look quite good.

So now I want the outside white, rather than the brown they currently are.
Can anyone suggest what paint to use to achieve this?
Will the previous brown wood stain begin to show through after awhile?

 

[Robbie uk]

The frame will no doubt be hardwood. Best to give the frames a very good rub down and then a coat of aluminium primer. Build up with undercoat and gloss as required.