Q.Is red mulch toxic to cats?
I just had an outdoor enclosure built for my 2 cats (12 x 12). A portion of it has old, red mulch and dirt where grass won’t grow. I’d like to put down a new layer of mulch to neaten it up. Is it toxic to cats?

The dyes used in commercial mulch is considered pet and kid safe.
Dogs that eat mulch is another issue and perhaps a call to your vet would ease your concerns.
Here is a link with more information.
https://www.gardeningknowhow.com/garden-how-to/mulch/keeping-mulch-safe-for-pets.htm