Have you tried placing a print statement after the if statement to see if it passes? If not then the part does not exist so I suggest printing part and the folder of parts where the suppose parts children.
If it fails the code will look like this
--print this after the line where you first define "part"
print(part, folder:GetChildren())
If you can not find the part varible inside of the table of the folders Children then it’s pretty obvious, the part varible is not correctly formated so it actual works.
You could also try to set the part varible to equal…
local Part = if (index % == 0) then "GreyPart" else "WhitePart"
One more question, why are you waiting on a for loop? Why can’t you just do task.wait(3)?