Sure, but a statement about beliefs can still be a statement of fact, rather than of opinion. For example, “I believe the sky is blue” is a statement of fact regarding the state of my beliefs. It can be false (i.e., I can believe the sky is red) or it can be true. Contrast, “The blue sky is pretty,” which is a value judgment I make about the sky, and therefore is an opinion.
A good way of analyzing it is to see if the statement would be contradicted by someone else holding the opposite view. So, if person A says “the sky is blue” and B says “the sky is red,” that’s a contradiction because they both can’t be true. But if person A says “the blue sky is pretty” and B says “the blue sky is ugly” then there is no contradiction–they’ve just come to different valuations.