If you look at the tennis courts in the early days of Wimbledon, or at a football pitch before the match begins, you may notice something nice about the grass.
Both arenas are tastefully arrayed with stripes, almost as if separate, alternating strips of carpet, about a metre wide and of contrasting but complementary shades of green, had been carefully laid upon the ground. But why? It obviously has something to do with the way the area is mown, but blades of grass over a small area must be, as a rough approximation, identical. And grass is green, not forty shades of it, or even two. Just green.
The answer lies in how the grass reacts to the light that falls upon it. Almost any object appears to be a certain colour because its molecular structure is such as to absorb certain wavelengths of light and to reflect others. In the case of grass, all colours except those which make up the colour green are absorbed; the unabsorbed green light is "rejected" and registers as that colour when it hits our eyes.
When sunlight hits a blade of grass at an oblique angle, however, light in all parts of the spectrum is reflected before the process of selective absorption can take place. This, as far as an observer is concerned, has the effect of overlaying the green with a whitish tinge; the green appears lighter than if the blade were viewed at some different angle, or than it would if not directly illuminated by the sun at all.
Mowing a lawn or a football pitch, particularly when the blades are followed by a roller, gives nearly all the blades mown in the one direction a common orientation; when the mower turns and cuts a parallel stripe the opposite way, these blades acquire a different, but again nearly uniform, orientation. The sunlight therefore hits the blades of grass in two adjacent strips at different angles, so they reflect and absorb light in differing proportions and therefore appear different to the eye.
Once play begins, of course, this careful orientation of the blades of grass is totally disturbed and the patterns quickly disappear.
If you rarely see the same effect on the patch of grass you call a lawn chez vous, it's probably because you mow the grass in a somewhat random way, and do not go up and down with care. Try it, and you may very well achieve the desired effect.