WASHINGTON — Of all the things that can make a person see red, school principal Gail Karwoski was not expecting parents to get huffy about, well, seeing red.

At Daniels Farm Elementary School in Trumbull, Conn., Karwoski's teachers grade papers by giving examples of better answers for those students who make mistakes. But that approach meant the kids often found their work covered in red, the color that teachers long have used to grade work.

Parents objected. Red writing, they said, was "stressful." The principal said teachers were just giving constructive advice and the color of ink used to convey that message should not matter. But some parents could not let it go.

So the school put red on the blacklist. Blue and other colors are in.

"It's not an argument we want to have at this point because what we need is the parents' understanding," Karwoski said. "The color of the message should not be the issue."

In many other schools, it's black and white when it comes to red. The color has become so symbolic of negativity that some principals and teachers will not touch it.

"You could hold up a paper that says 'Great work!' and it won't even matter if it's written in red," said Joseph Foriska, principal of Thaddeus Stevens Elementary in Pittsburgh.

He has instructed his teachers to grade with colors featuring more "pleasant-feeling tones" so that their instructional messages do not come across as derogatory or demeaning.

"The color is everything," said Foriska, an educator for 31 years.

At Public School 188 in Manhattan, 25-year-old teacher Justin Kazmark grades with purple, which has emerged as a new color of choice for many educators, pen manufacturers confirm.

"My generation was brought up on right or wrong with no in between, and red was always in your face," Kazmark said. "It's abrasive to me. Purple is just a little bit more gentle. Part of my job is to be attuned to what kids respond to, and red is not one of those colors."

Three top pen and marker manufacturers — Bic, Pilot Pen and Sanford, which produces Papermate and Sharpie — are making more purple pens in response to rising sales. School leaders and teachers are largely driving that demand, company representatives say.

"They're trying to be positive and reinforcing rather than being harsh," said Robert Silberman, Pilot Pen's vice president of marketing. "Teachers are taking that to heart."

The disillusionment with red is part of a broader shift in grading, said Vanessa Powell, a fifth-grade teacher at Snowshoe Elementary School in Wasilla, Alaska.

"It's taken a turn from 'Here's what you need to improve on' to 'Here's what you've done right,' " Powell said. "It's not that we're not pointing out mistakes, it's just that the method in which it's delivered is more positive."