The parameter that sets the colour of the border in the config does not change anything and the border stays red on the map.

...
# The hexadecimal color code of the world border shown on the map.
# For help with this, visit a site like https://www.color-hex.com/
color: FF0000
...

Using Dynmap on Paper 1.18 with the latest version of Chunky and ChunkyBorder.
There are no console errors during startup relating the either plugin.

Unable to produce this on Chunky 1.2.153 + ChunkyBorder 1.0.59 + Dynmap v3.3-beta-1.

Let me know if you have more specific steps which cause the issue, but otherwise I would recommend double checking that you've saved the configuration and have restarted the server for the changes to take effect.

There is also the Discord support server if you want to share your configuration for me to take a look.