If I am seeing what you are are describing, it looks like this might simply be the black edge of the film protruding from the slide mount. It looks like you have the "jet" black edge on the outer left, then a slightly less black strip, then the color part of the film. Look at the slide, I would guess that this less black strip is the area of the film beyond the emulsion. As for the color on the trunk....very difficult to comment on as I can't see the slide. I believe the Nikon scanner has a dynamic range that exceeds the film latitude. It's possible it's picking up something you have a hard time seeing on the very small slide. Regarding colors, this depends on lots of things. Don't expect what you see on the monitor to mirror what is on the slide, unless you have calibrated your monitor. Simply tweek any of the monitor controls and this will greatly affect the image you see, but not the color information in the image file. It may not be the scan that is off.