Why is the colour of the activity-number-flag changing?

I feel a noob for asking this, but I can’t find any legenda.

The tab-head Activity has a little coloured box that shows the number of downloads in queue.
What determines the colour of this box? It started red, then came orange, then blue, but now it’s red again. Does this colour tell me something?

These apply to items coming from your download client’s Queue/History.

Red = something with an error - failed download, something Sonarr can’t handle
Yellow = something with a warning (might be able to do something with manual intervention, in a future release)
Blue = Everything is operating normally.

Aaah, that explaines. Thanks.