You could use a sample spot (white, 50% gray or black) and use the eyedropper tool to set that value. This should also fix the white balance. (...) A cheap and dirty way is to simply include an 18% gray card in the images and grab your neutral gray from there.
+1
But the bundled Epson software might not allow this, unless you are prepared to include a gray card in
each shot. Your problem arises from the auto-everything mode of Epson scan software, more or less trying to make the picture color neutral
on the average.
Here is how I handle this with vuescan; then you can find out if a similar functionality exists in the software you use. One shot
per roll with a gray card (optionally also a Wolf Faust target, but that is another story). First scan that frame; right-click on the gray card. Color balance switches to "Manual", meaning that the RGB balance is frozen until further notice, such that the gray card is actually neutral gray. Scan the other frames on that roll; the software remains free to adjust the black and white points automatically, according to the histogram. If the light conditions change (sunny, open shade, tungsten, etc), you may need more than one "gray card shot".
And here is how I would handle it in post. The software I use --Picture Window Pro-- is not very widespread; just to give you the incentive to look for similar functionality in your software. Choose (out the two pics you show) the one with the "best" blue. With eyedropper, take a note of the RGB values on the shutter. Open the other pic, activate color correction tool with a 2-D hue diagram eyedropper; eyedropper click on the blue shutter; "pull" it in the diagram to the "good" value. You can also do it by trial and error, playing with the corrections and checking the RGB value of the shutter; but this does not guarantee that
all colors are correct.
