A lot of people ask me, "Patrick, how do I keep my grass green?" Well, the most important thing to keep your grass green, is you're going to have to water it from time to time. As a rule of thumb, grass needs about an inch of water per week, so if mother nature is not providing the inch, you're going to have to help her out, and go out there with a hose and a sprinkler, and add some water.
Another tip to keeping your grass green, is to mow high. Set your mower on the highest setting that you're comfortable with, and looks good for you, because long grass blades shade the ground, which prevent weeds and keep the water from evaporating from the soil.
Another tip I can offer you to help green up your lawn quicker in the Spring, is to fertilize in the Fall. And when I say Fall, I mean really late Fall, like around Thanksgiving, while your grass is still green and photosynthesizing, but before it has gone dormant. If you add a final application of nitrogen, the grass will take up that nitrogen, and turn it into carbohydrates, store it in the grass. It will allow it to green up quicker in the Spring time. Think of it as your grass putting on winter fat.
So, if you want to keep your grass green, make sure to mow high, water frequently, and fertilize in the Fall.