Looking from my upstairs window i can see almost my entire streets back gardens.
Almost all of them have greyish wooden fencing panels, but i'm sure this asn' by choice.
what caused this so i can avoid it in the future?
Wood – Why do fence panels turn grey
fencewood
Related Solutions
A few options (ordered by relative ease):
buy the premade section and cut to fit
use regular 2x4 (1.5x3.5) material and ignore the size difference
find a tablesaw and rip stock to the exact size you want
Alternately, you could run the panels full width and fill in any gaps at the bottom with triangular pieces.
I've had great luck with expanded vinyl beadboard. It comes in sheets that can be used as paneling, pieces cut to smaller sizes for wainscotting, and planks. Some are reversible, with a bead on one side and a V groove on the other.
Expanded vinyl is the material used for most "permanent" house trim. It is a little more expensive that wood-based alternatives, but it is durable, lasts forever, and has better characteristics in virtually every respect. It's weatherproof, moistureproof, and unaffected by UV. It doesn't warp, rot, or split. The material inhibits the growth of mold, mildew and bacteria. It doesn't require painting but is paintable. It's easy to work with, and looks like the wood product. The rigidity is closer to thin wood boards than to paneling or plastic sheets. I've used it for exposed exterior, protected exterior (screen porch ceiling), and inside use (wainscot).
The big trim manufactures like Azek sell it through building supply stores: https://azek.com/products/trim/beadboard-trim.
Stores like Home Depot and Lowes have in-house brands: http://www.homedepot.com/p/House-of-Fara-W96WP-12-sq-ft-White-Vinyl-Reversible-Interior-Exterior-Paneling-3-Piece-per-Pack-W96WP/205437105
Best Answer
It is possible that some of your neighbors decided that a natural patina of weathered grey looks appropriate on their fence boards. The dulling of wood fibers occurs if the fence boards are left un-sealed or bare for several seasons. The greyish white tone that develops is mostly due to the bombardment of U.V rays from the sun. Without protection the wood fibers become dry and bleached. With the proper wood sealer and maintenance you can extend the life that a wood fence lasts for many years. If the fence is frequently subject to water (as when a sprinkler soaks it) the minerals in the water can tint the wood white when the water evaporates.