my friend said maybe its like morph from deluxe paint but he's more a coder than an artist.
so concept is it compares frame 1 and 2 for colour changes in each pixel, adds a smoothing frame which finds the nearest in-between colour (from the restricted palette importantly) and applies the colour accordingly.
if the idea works i could probably code it in GM but it would take me longer than someone who's good at coding
from what ive seen i cant think why the results wouldn't be awesome and time saving.