Do you see the different colours in this row of tree spinach (Chenopodium giganteum)? Not the magenta highlights near the stem tip of each plant but the range of greens, from the dark leaves on the left through to the lime green plants near the centre of the frame. Sometimes this effect in a photograph is the result of lighting but here it is intrinsic to the plants themselves
I suspect the cause is the different soil profiles underlying the bed. As you may recall from other images of our back garden, the landscaping has undergone several changes during the past year. I think this section shows two zones; land that was deep dug through with soil and compost (I originally had a raised bed planned for this section) and then soil that was originally lawn and not dug over so thoroughly. The latter is marked out by the yellower plants.
Overall, it provides a vivid illustration of just how important the soil is to plant development.