I have dark blue veins visible under and at the side of tongue. nthng more. is it normal.?

yes. I take it you never bothered to look before?

Yes, it is normal. You may recheck every month or so. If there is a change, you develop a sore, a swelling or discharge, see a doctor. Have a healthy diet, exercise 30 minutes/day, drink plenty of water daily so your urine is mostly colorless, have safe sex, no tobacco alcohol weed or street drugs. For nutrition: http://www.choosemyplate.gov/. Get HPV and Covid vaccines. Wish you good health!