Does the camera you shot them with have a BW or monochrome setting? Is it on?
Do you have another app that you can open them in? Are they still BW there?
My bet is the first instance, but that is because I did the same thing and it took a bit of tinkering to find it.
Ok sounds like you may have inadvertently set an import preset or default.
What does it say in the History of one of the b+w files???
You can select all and use the v key to change them all with autosync on.