Refer to figure.
EASA learning objective 022.12.10.01.18 states: 'Explain the indications of a TA and an RA and how an RA will generate a red area on the VSI. Some variants will also include a green area. To manoeuvre the aircraft to comply with the RA, the pilot should ‘avoid the red’ or ‘fly the green’'.

When an intruding aircraft, with a transponder that's transmitting altitude information, poses a collision threat a TCAS II system will generate a resolution advisory (RA) which commands a manoeuvre in the vertical plane when necessary. TCAS II RA commands are aural ('climb...', 'descend...' etc) and visual, with required rates of climb and descent being displayed to the pilot on the VSI. RA commands must be followed, no ATC clearance is required, RA's override ATC instructions.
PFD equipped aircraft use red and green bands displayed on the vertical speed tape and TCAS traffic is displayed on the ND. The green arc represents the recommended vertical speed to be maintained during an RA and a red arc on the VSI scale indicates climb and descent rates to be avoided. Aircraft without EFIS use an EVSI to display traffic as well as the red and green bands.

The figure in the question shows the green band indicating the rate of descent required during a TCAS RA, as the LO says: 'Avoid the Red' or 'Fly the Green.'

Note: Traffic advisories (TA) do not issue avoidance commands.