hi my name is Anushka Sharma and I want to ask the question my question is we use black and blue pen but whenever we underline the line with which pen black, blue or red

If it is the answer which you have written with blue pen then you can underline it with black pen and if you have written it with black pen then underline it with blue one red pen will be giving a vibe like the teacher has done it if the spelling or the answer is wrong.