If you have a 4x4 array of frames like that, you will paint the vertex colors as follows :
4x4 = 16 total frames
frame 0: 0/16 = 0
frame 1: 1/16 = 0.0625
frame 2: 2/16 = 0.125
frame 3: 3/16 = 0.1875
and so on.
Of course sometimes due to rounding errors you have to go slightly above or below those values if your frame counts aren’t powers of two. You can also just put a scalar multiplier on the vertex color that is defaulted to 1.0 to allow for quickly pushing all the values in case that pops up anyways. You don’t want to have to go repainting all the values.
Btw for this type of thing I am using procedural mesh these days so it can just spit out whatever vertex colors automatically. I can post something on this soon.