If memory serves:
On VHS tapes, there were typically three different recording speeds: SP (about two hours/best quality), LP (about three hours/decent quality), and ELP (about six hours/low quality). If the recording speed was longer than SP, the lower quality video might be what is causing the loss of color when trying to digitize.
Again, I'm just guessing here and not being too helpful in resolving the issue.
-Wolf sends