Jasper Chart Theme without Java knowledge

Jasper Chart Theme without Java knowledge

I found some older (outdated) solutions extending a special Java class to
build a new theme. I am using Jasper without Java knowledge and wonder if
(since version 5.3 of the server is out) there is an easier way of
applying new colors to the charts.
Is there a ResourceDescriptor able to hol a color theme? Like the
properties' one?
I use the REST (2) API, but no Java at all. Did possibilities change now
in the last 4 years?
Basically I want to use the aegean theme but apply some different colors.