I have almost never watched any tutorials. Any I did watch was largely to be ready to ridicule it. I tried googling the words we're using but found nothing except one video that has been lost.

You need to learn how to make materials and there is a lot to read or watch for that.

You need to learn how to animate a parameter - I believe there are things to read or watch for that.

Then you put the two learnings together - you make a material with a parameter that controls the progression of gray to red, for example and you animate it. Like this one: Here I made a shader that has one parameter that controls a random spot pattern of red and gray. The threshold goes from 0 to 1. When it is zero everything is gray. When it is one everything is red. I made this parameter animated (changing over time) by clicking the little key icon. Then I moved my timeline to where i want the transition to start, set the threshold to .01, moved my timeline to where I want the transition to end, set the threshold to 1, and I'm done.

Here are renders of a sampling of the animated frames over time.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)