Colored Sun in the Black and White Seventh Seal?

I have a question for owners of any DVD (especially the Criterion, but any DVD that might be relevant) of The Seventh Seal.

Three scenes were shot outside, including a long one where Mia and Jof the clowns are having strawberries and milk with the knight. On my DVD, I've noticed something I did not notice on first watching. Sometimes the sky is shown in the background, and the sun appears to be in the top-right-hand corner of the screen, only captured fuzzy, as a patch of light rather than as a circle. That in itself does not bother me; the scene was shot outside, so they would have caught some of the sun, and would have had to mute it in some way where the camera angle necessitated that it should appear on screen. But what is puzzling is that this patch of light is clearly YELLOW -- in a black and white film! It's a faint yellow in some places, brighter in others, but it's definitely the color yellow, appearing over several minutes of the film. I'm wondering if this is a defect in my DVD, or if others with the Criterion DVD (or other DVDs) have this definitely yellow patch in the top right hand corner where the sun seems to be located. If others experience this, then my DVD is fine. But then the question arises: how can any color be present in a black and white film or DVD?

Any illumination (no pun intended) on this point would be appreciated.