OK - good beginning to know what you are doing - no scanner - camera reproduction to raw converter. I don't know Leaf Capture, but in LR4, if you can't find any area in the photo that should be neutral and on which you can apply the white balance eye dropper, you can try the individual color curves in the Tone Curve Panel (not available in LR3, but definitely doable in Photoshop), as they may be able to neutralize the colour shift that has taken place over the years. I'd start with the Red channel. In Photoshop, again in the curves tool, if you can locate a point in the photo that should be black and set that point to black in each of the three colour channels that often does the trick completely. This problem should be capable of resolution without doing conversions in and out of LAB space.