The movie color conversion matrix (RGB -> YUB) for the EOS-1D X and 5D mark III has been changed to BT.709 (sometimes referred to as REC.709) for Full HD and HD movies (On previous EOS products it was BT.601). SD movies remain as BT.601.
Therefore it is recommended that editors use the new version of the EOS MOVIE Plugin-E1 for Final Cut Pro (Ver. 1.3) that supports a BT.709 color conversion matrix when using Final Cut Pro 6.x/7.x for editing.
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Via Thierry Saint-Paul