WD (Western Digital) hard drives have different colors for different meanings.
BLUE COLOR
The blue color means that the hard drive is universal, reliable and energy efficient.
RED COLOR
The red color means that the hard drive is designed for NAS and RAID systems.
GREEN COLOR
The green color means that the hard drive uses less power and is also similar to blue hard drives (they are no longer popular today).
Image source: https://www.hwcooling.net/en/test-of-six-hhds-from-wd-which-colour-is-for-you/
BLACK COLOR
The black color means that the hard drive is very powerful and is made for playing games and creating content etc.
PURPLE COLOR
The purple color is intended for storing data and videos recorded by the surveillance system (security cameras).
GOLD COLOR
Hard drives with gold color means that it is a high-end version of WD (Western Digital) hard drives designed for data centers and long-term storage of large amounts of data and other similar applications.