"BP Write Buffering" ratio calculated as Innodb_buffer_pool_write_requests/Innodb_data_writes. It shows how effectively InnoDB Buffer Pool is used regarding writes. If number of InnoDB Buffer Pool write requests is significantly higher than number of disk writes - performance is good, options and hardware are effective for the workload.
However, PMM displays colors in opposite order. Currently threshold is set to 3,5. So if ratio is less than 3 (bad performance) it displayed in green color and if it is greater than 5 (good performance) it is displayed in red color.
How to repeat:
open https://pmmdemo.percona.com/graph/d/mysql-innodb/mysql-innodb-details?panelId=119&fullscreen&orgId=1&refresh=1m&var-interval=$__auto_interval_interval&var-node_name=ps8&var-crop_host=ps8&var-service_name=ps8-mysql&var-version=8.0.19-10&var-crop_service=ps8-mysql&var-environment=All&var-cluster=All&var-replication_set=All&var-database=All&var-node_type=All&var-service_type=All&var-schema=All, check graph definition
Inverse order of colors. Also, change green color to white, because ratio > 5 on modern hardware is not bad, but could be much better.