World Autism Awareness Day 2015: Why People Are Wearing Blue Today

— -- Being a little blue never felt so good. You may have noticed there are a lot of people out there wearing blue today and tweeting selfies with the hashtag #LIUB for "light it up blue."

Today is World Autism Awareness Day, and even global landmarks like the Empire State Building and the Prince's Palace of Monaco are celebrating with special blue lights for the occasion. The United Nations declared April 2 World Autism Awareness Day in 2007, and we've been celebrating it ever since.

Autism is a developmental disability that usually manifests around the third year of life, according to the U.N. Symptoms vary widely across the spectrum but generally include engaging in repetitive behaviors, and having difficulties with communication and social interactions.

It affects all ethnic, racial and socioeconomic groups, according to the U.N.

One in 68 children born in the United States is diagnosed with autism spectrum disorder, according to the Centers for Disease Control and Prevention, which released findings based on 2010 surveillance data.

Parents are often the first to notice the symptoms, such as when a child doesn't make eye contact, according to the nonprofit Autism Speaks. Concerned parents shouldn't panic, but they should have a talk with their family pediatrician, experts say.