Scanning a color neg is a totally different ball game than scanning a print. In the analog process you have to use different filter settings for different brands of paper AND different brands of film. Then on top of that there are the various corrections applied for the "errors" in lighting the scene in the first place. The scanner has an automatic exposure and color balance routine, which in most cases you can influence at the time of the scan, for both reflection and transmission copy. Also the scanner has a different light source for each and needs its own tweaking between the two. So you can have prints looking fine and negs be off or vice versa if the calibration is off. Add to that the fact that you really don't know what the colors of the negative is before you scan it, unlike a print, simply because its negative color.
Looking at the rainbow shot, I'd say the lab messed up the color and you got the scan right but the tree looks good on the print and the scan looks too red assuming the bark is supposed to be grey.
Bottom line is you have to be the judge as to whether the color is right, you shot the picture.