"The chart test was a red and green chart test and he couldn't see the nuances of different shades of red or different shades of green within the chart test," Sam Lehr, Zachary's father, said.
A study of more than 4,000 California preschoolers finds color blindness mostly affects Caucasian boys with one in 20 suffering from the condition.
"The problem in color vision deficiency is on the X-chromosome. Girls have two x's, boys have one x. If a boy gets a bad x, he doesn't have another x, so he's going to be affected," Dr. Miesha Frempong, Mount Sinai Hospital, said.
The most common form of color blindness is genetic, people lack the genes that help the eyes see red or green. There is no reversal or cure for the inherited form of color blindness.
Dr. Miesha Frempong uses chips with different hues and color dot cards to diagnose patients.
"In order to see these numbers you have to see the color," Dr. Frempong said.
Researchers say in some cases color blindness can affect learning and test taking.
But in Zach's case, he's had no problems.
"It is a complete non-issue, and I don't expect it to be an issue going forward," Lehr said.