TL;DR
I take each RGB value for all Smash Backgrounds, and make 3 separate equations that are then mapped to a trendline.
I get the data to fit a trendline by adding all those values together. And having x represent the number of terms added, and y being those added terms. So... as an example... let's say x=1 and y =39. Then that means 39 is the first term and is only 1 term. If x=2 and y=48, that means that there are two terms being added and that 48 is the sum of 39 and 9, etc.
View attachment 322621
(Graph of the trendlines.)
I then take the trendline equations, find an answer and subtract it from the previous total to get an RGB value.
View attachment 322622
(Graph of the trendline minus previous sums.)
Technically speaking, this is an oversimplification, as you also have to factor in the movement of points around the trendline itself. But other than that, that's about it.