Need ideas how mix and match different edging stones
I am redoing our front yard landscaping - not one time complete overhaul, but several years step-by-step affair. Last year I bought white edgers (see picture) to lay border for the flower bed - currently black rubber edging. Last winter I had an idea to add a tall shrub in the middle of the bed, preferably in slightly raised bed. So now I have a vision of a circle with hydrangea in the middle and border going from it in both directions. I do not have enough white edgers for everything, so I will have to use some other edging material for middle bed. Any ideas how make it work? Right now I am torn between 2 options - either to buy white edgers with different structure/height/length or use similar elongated edgers of different, probably contrasting color. Not black, dark grey maybe - house is light grey and I have black mulch/dark grey slate rock in bed.
I would greatly appreciate your advice how to make it look planned not an after-thought. Thanks!
Picture of the front yard. Middle bush soon will be gone and I will plant hydrangea couple feet further from the house.