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I find it easiest to sketch using gray or black pencil - but I would like to be able to set a toggle on my layers to colorize them as red/green/blue etc, so that the black lines appear as another color, to make it easier to see all the different sections.

I know it is possible to change the color using the Sketch panel, but it would be preferable to do this "nondestructively," similar to the "Color Overlay" layer effect in Photoshop. It would even be fantastic to colorize according to the group colors, so I can choose to see on the TVP canvas which layers are in which group, without having to look at the timeline.

Humm, I'm not sure that I understood you properly, but aren't you asking for layer blending modes ?

If so, this feature does exist in TVPaint Animation 10 Pro. On your layer, you will notice the word "color". Click on that word and a pop-up menu will appear with a long choices list. Colorize and Tint are in that list.

Edit : OOOKAAAAY, I understood. You want to see your lines with the color of the layer's color group, isn't it ?

What he asks for is a viewing mode similar to the one in Illustrator (where the selected shape has an outline depending on the layer it's in). I can understand the request, but am not sure if that would help me. What I do is simply set all the layers I'm not drawing in to about 50% transparency. This way it's sorted for me: black = current, gray = anything else, colour = lighttable.

I remember Ryan Woodward also asked us for something similar.