I have the same problem, too. Stitching microscope images works quite well with ICE, except for that annoying color gradient!!
Here's what I think is happening: The microscope illumination is slightly uneven across each individual photo prior to stitching, e.g. more blue at left, more red towards the right side. When ICE stitches the photos together, it appears to extrapolate this
color gradient, effectively amplifying it in the final resulting panorama:
For example, take four photos in a row, which are all slightly bluish at the left, slightly reddish at the right:
Photo1 - Photo2 - Photo3 - Photo4
In the resulting panorama, the color shift will be extremely blue on the left (all of Photo1 is now blue), and extremely red on the right (all of Photo4 is now red). The original (natural) coloration of the photos is lost, especially at the edges of the
panorama.
How can this problem be avoided?