You did the PCR test... for today.
The result of this thing has a expiration period (in multiples of 24 hours) announced by the local government. For example, if they decide that it should expire after 48h, then you need to do this once every two days; if they decide that it should expire after 24h, you need to keep doing one every day, etc..
Now here's the fun part. Pick a color. Mainland Chinese will know what these colors represent, but you might not.