Hey Swaroop !
Generally there's no specific rule about the colour ink which is needed in order to write your Class 12 Board Practical Files and Projects but it is advised that the work should be done in a manner in which, it is uniform throughout the year.
Like, in our times, we were told to write the headings and sunheadings with Black Ink and the normal write up with Blue Ink, so that it looks elegant.
Also, we were told not to alter the order of the ink for the write-up and headings. And that, except Black and Blue, NO OTHER ink should be used.

Hope this helps.

All the Best !