Color modifier at object level (not material level)

I want to do a film explaining a machine with many components (gears, chains, pipes etc.) which basically are of the same material (e. g. metal).
In the animation I want to color-highlight (emphasize) the according components which are important in a certain time slot, namely when explaining, say, parts 1,4,5,7,8,34 of the machine I want to highlight those parts 1,4,5,7,8,34 etc.
E. g. make a single certain gear glow or strongly blink at a certain time, then make 10 others of the machine glow a minute later etc.

But I do not want to create a single new material for each component which I then may animate in color.
I could do that maybe in rendering layers via the compositor as I have understood (beginner) but they are quite limited in the layer numbers.
So for each difference in key frames in the color animation I would need to create a separate material. This would be tedious and unflexible and result in tens or hundreds of materials although in the default status they are all of the same appearance (e.g. metal). I just need temporary material modifications across thos many similar objects.

Is there something such as a ‘color modifier’ or material modifier’ which may be animated for objects? E. g. adding an ‘animatable’ glow (emission) or a color or a blinking effect at object level (not to a material) for a certain time?

You can give each object a Pass Index in the object properties. You can use that to create a mask in the compositor to change the effect on a select part of the render such as a specific object. In the render passes enable the Object Index pass and in the compositor use a ID Mask node to specify a pass index you want to use.


See the attached blend file for an example

Attachments

id_mask.blend (93.1 KB)

@Richard: That is a nice solution. Then the task just becomes animating the Pass Index for the object from 0 to 1 at the time the object needs to be highlighted.

I tried your blend file and it works fine. However in my scene the object pass index does not work. I assigned a pass index (Object -> Relations -> Pass Index) and enabled the render pass “Object Index”. However when trying to mask the object in the compositor it just does not work. I used the same setup from your blend file but the viewer node just displays the full scene with no color adjustments, no matter which object index I use.

Any idea what I’m missing?

EDIT:
Never mind, I found the problem. To get better lighting, I was using the backfacing option of a geometry node to make the camera-facing face of a cube transparent to the camera. This messed up the object index mask for the objects inside the cube.

I removed the face which faces the camera and now it works. But now my lighting is messed :frowning: