Why do some Shimano Scorpion 1501 reels have different spool than others? For example, some have a skinny silver while others have like a shiny purple. What is the reason for this?

@JustJames this question has your name on it

I don't know man, it is an old reel I have not born yet. Lol

 

My guess is regular scorpion 1500 come with deep silver spool, then there is different version SF? with quick fire light weight/shallower spool. Like chornarch version we have here.

Sounds like you're referencing two different reels.  The original 1500 was the JDM version of the Curado SF from the late 90's early 2000.   The 1500XT was the JDM Curado 200E from the 2008-2013 period.

 

Edit:  Forgot that Scorp 1500 was preceded by model that was the same as our 90's Curado B hence the deeper spool. I'm guessing these are the reels you're talking about.  Sorry about the confusion.  Side note:  Guys practically fight over good condition Curado 200E's while JDM 1500XT's go unnoticed. Maybe it's the funky plum color.

Isn't there a 50 size and a 100/200ish sized Scorpion? Perhaps you're seeing different models and noticing different spools and not that they're different sized reels.

First compact Scorp was the 1000 which is basically the Curado 100B and D with a different SVS system.  The only 50 sized Scorp was the 1000 XT which was the same as the Curado and Chronarch 50E.  Still a lot of love for these reels.