What is "temporary flight plan" in A320 MCDU?
The temporary flight plan is visible on the mcdu in yellow when you modify the actual flight plan. It will be shown in yellow as well on the ND (for modes ARC, NAV and MAP) until you press the 6R button of the MCDU, which mean * insert.
The goal is to let you see your modification before inserting it in your flight plan. Knowing that most of the time you will create a discontinuity in it and you will have to review and delete the discontinuity.
If you use secondary fplan you will have the information in white.