I had same problem with Fijutsu 5110C scanner. It scanned only to greyscale when used from AC. I solve this problem by switching from Twain to
WIA interface. Most scanners come with both Twain and WIA interface. WIA interface is much move convenient and faster to work with. You can easily switch from Twain to WIA by selecting the default scanner in the <Scanner Controller> window. All previous versions of AC worked fine with WIA, but the latest version 3.7.14 didn't work with WIA interface. I had to reinstall version 6.0 on top of 3.7.14 in order to keep my WIA scanning going. I contacted AC support and was told, AC only supports Twain scanning driver, but not WIA. Why? I don't know. WIA works so much better than Twain. I wish the new version of AC supports WIA, so I wouldn't have to reinstall old version 6.0 on top of updated AC again and again.
