Red color on recoil spring - rust or paint?

[candc]

Hi...this is my first time field trip my new handgun (sig sauer) after just 100 shots. I saw the first inch of the recoil spring is red color. not sure if it's rust or paint. Anyone knows what it is? thanks,

 

[FarmerDanz]

X5 legion?
It's the lighter spring the thing comes with two.

 

[candc]

it's sig sauer P320

 

[DavenK]

Sig uses paint on their recoil springs to indicate caliber/recoil force of the spring.