While I'm sure painting the fences can be successful, I would be careful painting the decking.

First of all I think you will need to wait a while after it has been installed before you paint/finish it, not sure how long, I'm sure your decking provider can tell you.

Secondly, I think actually painting it might be a little bit counterproductive. It will look nice to start with but I fear that the paint will wear, or even come off pretty soon after.

I bought some slate grey decking paint and have only used it so far on a number of wooden plant containers about a year ago. I'm glad I haven't done our decking with it; the paint is flaking here and there and wearing thin in other places.

Perhaps I didn't buy the most expensive stuff, but it was still a well known brand (Ronseal, I think it was).

A better finishing product / sealant might be decking oil.

Perhaps some food for thought for you... :)

Considering how narrow the garden is, I would avoid a really dark colour on the fence as it would make it feel even narrower. Since you are replacing the existing decking, perhaps a composite would be worth considering as that comes in a good range of colours.

Astro turf is good in some places but as mentioned if you are in an area where moles are prevalent, they can cause a lot of damage.

It needs a good compacted gravel base to provide drainage,then a weed proof membrane, usually the joints are epoxied with tape.

Are you using diagonals or curves to make the garden look wider? Would love to see a plan. Although painted fences can look striking (with dark aubergine probably making plants stand out the most) I would avoid this as it may narrow the proportions even more. To shorten the garden visually you could plant something like a chocolate coloured vine across the back.

I agree that dark colours would make the garden seem smaller. I love the look of the bright blue fence posted above!

I'm not speaking from experience, but I have read somewhere (likely here on Houzz) that very dark colours (black, anthracite etc) tend to 'disappear' in the background, meaning they actually make the space look bigger.

Either way I think it is probably best to incorporate some 'tricks' in your landscaping plans to limit the long and thin look of your garden somewhat. Maybe some zoning is a good idea.

You've possibly done that already?

Do consider a winding path rather than a straight one like the one you have now.

I think a winding path with shrubs and tall grasses at intervals would be lovely in your garden, and give a feeling of "what's around the corner?". If you are painting I would make the back of the garden and one fence side darker to create some width and depth. The other side could be a lighter colour like the blue or even bright orange if you want to blend with your neighbour's. I used Cuprinol Shades in Willow on one of my boundaries and it is beautiful winter and summer as a backdrop to planting , and in its own right. Don't use cheap stuff , you will rue the day when you have to repaint it all again because of flaking. A good quality paint in a couple of ciates will last 3 to 5 years. If you don't load the brush too much at the creases you will avoud runs going through the other side. Oil your deck once a year with a natural or lightly coloured deck stain and it will last and look beautiful . Enjoy