If you're using a SCART connector from your source, then it's possible
that you're unwittingly feeding an S-Video signal (which has separate
colour information) into your composite input. This would produce a
B/W recording.
I'm using a Scart adapter from the back of my VHS player, the scart adapter has a composite out, I then have a phone lead running from the composite out to the composite in of the capture card. The scart adapter also has an S-Video output, so I tried connecting that to the SVideo on the capture card, and it was still black and white.
I've now tried the Windows software on the windows partition of the computer, using the composite leads as described above - the result was in colour! I then rebooted back into Fedora, but the output is still B/W!
Thanks,
Jonny