While there is no universal rule, red ink has traditionally been used by teachers to mark errors in student work due to its high visibility. The contrasting color helps draw the student's attention to mistakes and makes it easy for them to identify areas that need improvement.
Additionally, the use of red ink for corrections has become somewhat standardized over the years, making it a widely recognized indicator of feedback and corrections in educational settings.
However, individual schools or teachers might have their own preferences regarding ink color for corrections. Some teachers may choose to use different colored pens for different types of corrections or comments. Ultimately, the choice of ink color for correction is up to the individual teacher and may vary based on personal preference or institutional guidelines.