The colors in the "Total Reach" column in the "Current stock" menu item adjust according to the status, as shown in this figure:

"Critical" (RED) = stock reach like lead time or smaller

"Low" (YELLOW/BEIGE) = Stock reach between Lead time & Lead time + Safety Buffer

"Good" (GREEN) = Stock reach between (Lead time + Safety buffer) & (Lead time + Safety buffer + Restock Freq.)

"High" (Light Blue) = Stock reach between (Lead time + Safety Buffer + 1x Restock Freq.) and (Lead time + Safety Buffer + 2x Restock Freq.)

"Overstock" (Dark blue) = Stock reach greater than (Lead time + Safety Buffer + 2x Restock Freq.)

The total reach tells you how many days of inventory you have left.

So: total stock (warehouse + FBA) / sales speed = total reach.

FBA reach tells you how many days of inventory you have left in your FBA warehouse. Normally, the incoming stock is also included here.