for admit card we should sign and put thumb impression from which colour for neet 2020

Only blue ink is accepted for giving Thumb Impression. You must put your left thumb impression in the Neet 2020 Admit Card with blue ink only. But make sure the thumb impression is clear and not smudged.
Along with this your parent's have to sign the Neet 2020 undertaking with blue ink in the space provided there. Check out this link http://medicine.careers360.com/articles/nta-neet-2020-admit-card-undertaking
Due to this pandemic, you must cover your nose and mouth properly with a mask. Put gloves on hands and take a small sanitizer bottle along with you. You must carry your own water bottle which should be transparent. Carry necessary documents such as Hall Ticket, Valid ID Proof, passport photographs etc inside the examination hall. Any other items are not acceptable.