This is the newest 2022 version which is Grey.
This fits all versions of Reverb from 2013 to 2022 and replaces the Blue version which is now obsolete and out of date.

Genuine Rockshox Reverb IFP (internal floating piston)
The new piston resolves the issue of the post sagging. 

Don't forget your other Reverb service parts....
Fluid - Ebay item number 283899897136
Seal Head bush and seal - Ebay item number 284240502217
Sram Butter grease - Ebay item number 283870508786
200hr service kit - Ebay item number 283836379353
Top Cap - Ebay item number 284983597003