The "This is a good candidate for FastPass+" tag shows up on all steps with a wait time over 15 minutes. This simply tells you that it would be nice to have FastPass+ for that step since the wait isn't short.
The green note is not necessarily a recommendation of the best FastPasses to get. For that, you should look at the "Advanced Options" in the FastPass+ Selections part of the screen; if you input the number of FastPass+ selections you can access in each group, after you click Optimize you will see a rank-order list of recommendations where FastPass+ would save you the most time.
Please note that neither the green warning nor the rank-ordered list of FastPass+ recommendations implies that you can get that FastPass+ or that your day will be ruined if you're in the standby line for that attraction.
In addition, we provide general FastPass+ recommendations here: