If you want a lawn that is a deep, lush green as much of the year as possible, then you are going to need to do some serious planning ahead of time to make that happen. Deep green grass is fairly easy to keep up once you have it, but you need to plan -- and plant -- appropriately as well as use the right maintenance techniques in order to get that bright, deep color that you want.
Pick the right mix of grass seed. When you plant grass seed, a mixture of seeds are best to keep your lawn lush and deep green under any circumstance. Make sure that the seeds are deemed "climate appropriate" for your area. You may need "warm season," "cool season" or both depending on what the weather and temperatures are like where you live.
Water carefully and regularly. Water your grass regularly, but always do so in the morning so that the water does not sit on the grass blades in the afternoon or evening and provide an ideal spot for mildew and mold. Water when the ground is dry, but do not water daily unless it is dry every day or you will train your grass to grow shallow roots, which makes it susceptible to a variety of spotting diseases that will discolor your lawn.
Maintain your mower and your mowing patterns. Keep the blades on your mower sharp so that it does not rip up the grass, which creates patchy, discolored bald spots. Generally you should not cut grass shorter than 2.5 inches or leave it longer than 3 inches. This allows grass seeds to fall on the lawn but does not cut the blades so short that you actually harm your turf. Alternate the directions in which you cut so that the grass clippings do not pile up too much.
Fertilize your lawn with the "magic 3." These three fertilizer ingredients will provide your lawn with the nutrients it needs to stay a deep, luscious green. Your fertilizer should contain nitrogen, potassium and phosphorous, and you can apply it to the lawn multiple times throughout the growing season.
Rake up grass clippings. This helps grass seeds root and sprout more quickly and prevents your lawn from "paling" as the dead clippings become more visible over the course of the summer.
Keep off the grass. When you first plant your lawn and it sprouts you probably are overjoyed at the emerald expanse you have created by staying off the lawn and babying the yard. However, once the grass starts growing, you probably start walking around on it. If you really want to keep your grass a deep green, then you need to limit traffic on it as much as possible.