Oahugirl,
Welcome to The Gardener's Forum, A Cybercommunity of Gardeners from around the world.
Questions:
What type of grass is in the lawn?
Manienie or Mahiki, some type of Zosiagrass like templegrass or Koreangrass, St. Augustine?
Is the lawn in shaded area?
Is there a sprinkler system and how long do you do the watering? Is the soil damp or wet most of the time?
Was the soil amended with organic matter, such as manure, leaves, grasss clippings, compost, bagasse, peat moss, or hapuu before putting the grass down?
What is fairly new? Six months? One year?
Yellowing may indicate Nitrogen or iron deficiency, or improper pH level, but there may be other factors such as virus (St. Augustine grass,etc.).
Papito