

Skelion is a plugin of SketchUp. It means you need SketchUp running on your computer
to install it. Follow the normal procces to install plugins on Sketchup (Watch manual or SketchUp online help).
Requirements:
Sketchup Pro or Sketchup Make 2017
(Reload the page if link doesn't work. Use "save link as" to save as .rbz and avoid automatic unzipping.)
By purchasing a Skelion license, you will automatically receive a Skelion Pro & Support Package for a year. To keep benefiting of it you can annually renew the package.
Insert your email. You will receive an email to activate Trial version.
If you need the functionality of Color Efex Pro, the best path forward is to look at modern alternatives rather than trying to revive a version from over a decade ago.
Finding a legitimate Nik Software Color Efex Pro 3.0 serial number today can be challenging. Because the software has changed ownership multiple times—from Nik Software to Google, and finally to DxO—the original activation servers for version 3.0 are largely defunct. Users looking to restore their old workflow often encounter "invalid key" errors or find that their original boxed copies no longer register online. The Evolution of the Nik Collection Nik Software Color Efex Pro 3.0 Serial Number
DxO offers a modern, fully supported version of Color Efex Pro. It includes high-resolution interface support, non-destructive editing, and compatibility with the latest versions of macOS and Windows. If you need the functionality of Color Efex
Nik Software Color Efex Pro 3.0 was a revolutionary plugin suite for digital photographers, offering a vast array of filters for color correction, retouching, and creative enhancements. While it has since been succeeded by newer versions within the Nik Collection, many users still seek ways to activate older versions they may have purchased years ago. Users looking to restore their old workflow often
Using unauthorized serial numbers violates software license agreements. How to Get Color Efex Pro Legally Today
If you are a legacy owner of version 3.0 and lost your key, contacting DxO support with your original proof of purchase is the only official way to attempt a recovery, though they may suggest upgrading to a modern version for a discounted price. Conclusion
For a time, Google released a version of the Nik Collection (Version 1.2.11) for free. While no longer officially hosted by Google, some reputable photography archives still provide the installer, which often does not require a serial number for activation.