When sophomore Mark Ahrens was in kindergarten, he used watercolors to paint an underwater scene — it had fish, a cruise ship and a bright yellow sun. He proudly hung it up to dry in the classroom and was then approached by two inquisitive girls in the class.

“[They] asked me “Why’d you paint the water purple?” Ahrens said.

He later learned he is red-green colorblind, the most common form of the disorder, which causes people to confuse seemingly similar colors. People with it do not properly perceive red and green and also confuse colors such as blues and purples, and reds and oranges.

“Until a couple years ago I thought I was more ‘color stupid,’” he said. “I thought I could see the differences

between colors, but I never really learned which one was which.”

Ahrens’ story is not uncommon. Colorblindness is found in about one in 10 males. It can be caused from missing pigment in the nerve cells of the eye, called cones, and causes people to perceive colors differently than those with normal vision.

Though it causes a difference in color perception, red-green colorblindness has no effect on visual acuity. Ahrens says he has 20-10 vision, which is better than the near-perfect 20-20 vision.

“[Colorblindness] is just a little quirk of mine,” he said.

Colorblindness is typically discovered during childhood while learning colors, though sometimes people spend a lifetime without knowing they have it. Senior Paul Cataldo learned he was red-green colorblind while in middle school.

“It was kind of weird because it kind of throws off everything you thought,” he said. “…Obviously what I see as red is red to me, but to everyone else it’s a different shade of red. I don’t know what everyone else sees. It would be interesting. It’s just a little different to know that what I see is different than everybody else.”

While it’s common to have at least one colorblind male in every small classroom, only about one in 250 females suffer from the disorder. This is because of the way genes are distributed — females carry it, but rarely suffer from it.

Dr. Paul Kempkes, an optometrist at Sterling Optical in Ithaca, N.Y., said colorblindness is a recessive gene. Females who carry the disorder have a 50-50 chance of passing it onto their sons.

“Colorblindness is a sex-linked disease that’s on the ‘X’ chromosome of the ‘XY’ pair in males,” he said. “If males get one of those chromosomes on the “X” side, they’re colorblind.”

Though red-green colorblindness is the most common, the disorder takes on many other forms, such as the handicapping ‘blue-yellow’ colorblindness, in which vision is so poor that its sufferers need to squint even in daylight. The rarest kind of colorblindness, Achromatopsia, has symptoms that include severe light sensitivity, causing those who suffer from it to see only shades of grey.

While the disorder is often easy to adjust to, it causes problems in everyday tasks. Getting dressed raises questions on matching clothes; buying a car needs color confirmation. Cataldo faced this problem as a teenager.

“During middle school and high school [is] when I first kind of realized I might be making a fool of myself when I go to school,” he said. “In fact a couple times in high school a few friends approached me jokingly and said ‘You probably need to go home and change ’cause you look like an idiot.’”

Driving is another facet often hindered by colorblindness. While Ahrens said he does not have a problem driving due to the typical placement of stoplights, Cataldo said he has to be careful when approaching yellow-red blinking lights since they are not easily distinguishable.

“I’ll always slow down,” he said.

Despite its challenges, Cataldo said he has come to terms with the disorder.

“I know what I know, and I see what I see,” he said. “Sometimes it’s [funny] to other people [when I say] ‘Look at that green thing over there’ and they say ‘What are you stupid? That’s red.’ It’s something I’ve definitely dealt with for a while.”

There is no treatment for colorblindness other than certain vision-altering contact lenses. Kempkes commonly tests for the disorder using the Ishihara test, a series of colorful circular designs with embedded numbers. People with normal vision can distinguish certain numbers in the tests’ designs, but to the colorblind, they appear as spotted, almost psychedelic-looking circles, or another number altogether.

“It’s a little book of like 15 different plates,” Kempkes said. “You look at it, tell me what you see, I look up the answers in the back of the book and that tells me what kind of colorblindness you have or if you’re normal.”

Kempkes said he does not force the test. It is so common that he only performs it when asked.

“Most people coming in who are colorblind sort of know it ahead of time,” he said.

For many with colorblindness like Ahrens, the largest inconvenience is being quizzed on the subject.

“If I’m saying it to just a couple people they usually say ‘What color is my shirt? What color is this? What color is that?’ which gets freakin’ annoying,” he said.

But it’s a question he’ll likely hear for the rest of his life.