I can't get a straight answer from them on this.

I would love to put a laser guide rod on one of my Sig P226's in 357 sig.... but I would like for it to be a green laser...

They only offer them in red for the this... but they do offer it in green for the 9mm ones... So, I asked them if the only difference was the recoil spring. (laser guide rod being the same why not have a green laser rod with 357 spring?

Are the two barrels that different, I know the slide is a little heavier... but I have traded the upper on two of my Sig P226s... 9mm & 357 sig.

Can't speak for your individual application, but one thing I have come across is the breech block is different between different calibers.
Not sure if the machining is different for that or the take down lever axis. It is different between a regular P220 and the 9mm P220.

One other thing I had issues is the overall length of the laser, but that was more likely a variance in the 1911s I was swapping them in.

Let us know how it turns out.