A healthy lawn will have a lush appearance and a bright-to-dark green color when they are healthy, well nourished and in their prime. Your lawn should be a lovely deep bright green color. If it is not this color then you probably have an issue. Light green or yellow grass is an indicator of an issue, although it can be very difficult to pinpoint what this issue is as there are a few different things that could possibly cause this problem.
If your lush green lawn starts to discolor you will need to consider an array of aspects to the growing conditions of your lawn, as well as your management practices of your lawn in order to conclude the most likely cause of the discoloration.
The most common cause of discoloration is simply a lack of water, which is much more common than you may guess. Lass grasses can suffer from something call ed moisture stress, and they will wilt before they turn yellow. You may not notice wilting in closely mowed lawns, hence discoloration may be one of the first signs of this. To resolve this simply irrigate the lawn. However, do keep in mind that residual soil moisture varies from one patch of your lawn to another, so it is possible that irregular areas of poor coloration can actually be caused by moisture stress. If you have a sprinkler you should confirm and check that the sprinkler distributes enough water to all parts of your lawn equally.