Sillkens make a product for exterior wood that looks good and gives better protection than just oil , it is "Cetol Filter 7" , there is also a wattyl product that I have had success with , " Wattyl Exterior Clear"
Have used both on western red and am happy with them both.
Both are for external wood in sun and weather and let the natural colours shine through, the wattyl gives a glossier finish.
If you have issues however with the colour change in diffrent areas of the windows you could try a coat of stain bringing the lighter areas up to match with a couple of coats and the darker areas with onle a thin coat, food for thought anyway
Rgds