[YepYep]

You are right. The portrait does have two different eye colors.

Makes me wonder...does Trump in real life have the same color in each of his eyes??

[Sisku Hanne]

I think one eye looks darker because it is in shadow. The light strikes the other eye at a different angle and reflects. His eyes are light in color so the effect is more noticeable.
I think his eyes are probably a pale grayish blue, which can appear to change color depending on what he wears. That's what mine do.
The artist painted the portrait using an Old Master technique called "grisaille", which uses an underpainting of one color. Then sheer layers of color are applied over top of the underpainting to develop the final painting. He used a warm sepia brown as his underpainting to infuse the portrait with an overall golden glow.