I’ve never been happy with my results using the keyer in FCP. I usually use Keylight in AE. Since you have it, why not key there? Motion has a much better keyer (Primatte) than FCP. If someone can’t help with the FCP key, try Motion. At least you can round-trip from FCP.
John
MacPro 8-core 2.8GHz 8 GB RAM OS 10.5.5 QT7.5.5 Kona 3 Dual Cinema 23 ATI Radeon HD 3870
ATTO ExpressSAS R380 RAID Adapter, PDE Enclosure with 8-drive 6TB RAID 5
24″ TV-Logic Monitor
Final Cut Studio 2 (up to date)
Pro Tools HD w SYNC IO, Yamaha DM1000, Millennia Media HV-3C, Neumann U87, Schoeps Mk41 mics, Genelec Monitors, PrimaLT ISDN