In the movie Portrait of a Lady on Fire, the character Héloïse has blue eyes, but in a particular scene, we see her eyes turn pure black in color. In the background, we can hear Marianne saying "Your eyes", and the scene ends there.
What is the significance of Héloïse's eyes turning black? When I googled about the color change, the results said that a person's eye color changes to black when they are angry, but there's no way Héloïse was angry at that time.
Look for the symbolism in the scene, usually black eyes are associated with psychic powers and being able to tap into dark energy, Héloise used to be in a convent, a religious place, and turned into the dark side in a manner of speaking. That's why the whole scene is into the paranormal, the same way Marianne is haunted, it's symbolism for forbidden desire.
A common effect of certain drugs is dilated pupils. In this particular seen they have just rubbed a paste on their arm pits that is meant to make time seem longer. Likely some type of hallucinogen.
It is possible the scene portrays a dual meaning as it is said when you look at something you love, your pupils grow bigger. The scene cleverly hints that they feel love, or have just made love.
