Dear student,

Central Board of secondary education has releases several guidance regarding board examination and the things need to be concerned while writing examination papers. One of those things is the usage of blue and black pen. It can be either gel or ball point pen. Mostly ball pens are preferred.

See, the restrictions are only for any other colors except blue and black. So it doesn't matters if you have use black pen for headings and questiins answer marking.  Actually you have done very good by marking the headings and questions with black pen. It improves your presentation.

Hope this information will help you. Thank you and very good luck!!!