Greeting ,
Now here is a very very simple solution to your wanting to add some sort of background to what sounds like what i call a flat canvas,
(All gardens are like a painting and background ie grass area's / hedging / even tarmac paths are all flat canvas area's)
I would give serious thought to keeping your garden as maintainance free as poss "but" this can still have life throughout winter and added colour during the warmer weather "be it by troughs full of flowers, Handing baskets again the likes of geraniums "these dont need a lot of watering day by day as they are a plant that likes dry conditions and sun,
But the common privet hedge sounds to me ideal for your needs,
Not only can these be kept to a small size growing in pots "But" they are not a fussy plant ref soil, and if you want colour then the common privet can be bought in bright yellow/darker green,
Now you've not said how long this path is ,? ie is it a threat to heathrow's new landing strip
But here is an idea i think you can see, one pot with common yellow privet hedge in and next to it another pot with Lavender (english or french)
and then the next pot common hedge and the next Lavender and so on until your at the end of this path,
Lavender again is'nt worried about soil, infact like the privet hedge this plant prefers rough soil , And you can grow them to about the same size they'll live together,
Ive this continued yellow priet hedge on one side of my pool and an Lavender full size border on the other,
Infront of the Privet ive verious sized tubs and clay pots / and between these larger tubs the sunbeds, the waft of the Lavender when you get that breezing evening perfume just has tobe experienced to know what im saying, but so simple to provide,
So you've now got a path thats a back ground to the tarmac "but" you've two plants you just leave in place winter/summer,
the Lavender has a very carm /relaxing perfume and both these plants have few if any pest that will bother them,
Now this and the trough idea plus hanging baskets with both herbs/flowers even cherry tomatoes growing hanging over the hanging basket through the summer along with the odd storm light hanging with the frame painted a nice bright colour and the "T" candle in the light lit near your sitting area a glass of wine and the summer evening coming to an end, what more can you ask,
Ps Hope this helps