If they are OEM springs for that particular model, they should have the same number of coils, be same approx length if they are unused. (they may or may not be colored, depending on age) I believe the green color (or blue) was added to some of the springs to differentiate between models the springs were designated for. You could also check the wire diameter if they are otherwise alike. (length and # of coils)
All the recently produced S&W OEM springs I have for my 6906 are green, and the wire diameter is .039". (Some of the older ones I have are not powder coated) Here's a photo of the spring at Midway......
Smith & Wesson Recoil Spring S&W 3953TSW 3913 3914 3914DAO 3953 3954