ID 164069 - Write node YCbCr Matrix doesn't grey out when default Pixel Format is RGB(A)

Set a write node to Prores4444, and the default Pixel Format is RGBA. This being the case, the YCbCr matrix should be greyed out, but it's not.

Setting a Pixel Format for RGBA manually does grey out the YCbCr successfully, so this only affects the defaults (ProRes4444 and Animation, for instance)

Repro:
- Open Nuke 7.0v80a13 and add a read node
- Set the codec to ProRes 4444 or Animation
>> The YCbCr Matrix is enabled, it shouldn't be.
Host(s):