In 2016, Google made the Nik Collection free , which included Color Efex Pro 4. This version does not require a serial number and is still available via the Wayback Machine on Lenscraft.
Nik Software Color Efex Pro 3.0 is a powerful plugin for Adobe Photoshop and Lightroom that offers a wide range of tools for enhancing and manipulating the color of your images. Released in 2009, this software has been a popular choice among photographers and graphic designers for years. Nik Software Color Efex Pro 3.0 Serial Number