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Hi, I'm a new user so please forgive me if this is a silly question but I'm finding it hard to find the information I need.
I would like to transition a CTG layer from black and white to colour across the timeline. I have been successful in applying the change that I want to the CTG squiggles themselves but the animation itself when played remains unchanged.
Is there something I'm missing?

Perhaps if you post a screenshot we could help you better.

You might have to make your CTG layer an animation layer before effects can be applied. As long as it's a CTG layer, it relates to the line art of another layer, and in the same line that you cannot use any tools other than the squiggle and erase on it, you probably cannot use effects, actually it's great that you get a preview nonetheless (if I understand you correctly). I recommend to duplicate the CTG layer to secure your information just in case, then leave one of them visible, make it an animation layer, and apply your effects to it.