Is this supposed to be blood?

From my experience playing this game, I don't think what you see is blood. There are extremes for different games, ranging from Call of Duty (ludicrous amounts of red jelly on your screen) to simple flashes when you take damage (think Hollowknight or similar). For No Man's Sky, your screen just starts to turn red as you take more damage, or alert more enemies.

Honestly though, the game is rated T for Animated Blood and Fantasy Violence, so based on your previous question, it might just be best to look for a new title to play.