When i add a colour grade effect to my footage it looks fine until i render.

[Michael Nielsen]

While your problem may end up having to do with 3rd party issues, before actually creating your sequence, you should be able to define a custom codec for preview rendering in the new sequence splash. There are three tabs in the splash, presets, tracks and settings. Inside of settings before creating the sequence you can select which codec to use for preview rendering, and only then. Not sure if it helps tho.