You can use a custom SVG, and rebuild with npm run build or, if you don't need to change the overall look, but just want to change some colors, put this in your app's CSS, and change any styles you like:
.ractive-gauge.mark1{
fill:none;
stroke:#a0a0a0;
}
.ractive-gauge.mark2{
fill:none;
stroke:#c0d0e0;
}
.ractive-gauge.center{
fill:none;
stroke:#c0d0e0;
}
.ractive-gauge.number{
fill:#606060;
}
.ractive-gauge.low{
fill:#fc172a;
}
.ractive-gauge.medlow{
fill:#ffe0e1;
}
.ractive-gauge.medhi{
fill:#e3ffe1;
}
.ractive-gauge.hi{
fill:#2cc71f;
}
.ractive-gauge.needle{
fill:none;
stroke:black;
}
.ractive-gauge.label{
fill:#707070;
}
.ractive-gauge.value{
fill:#707070;
}
These are just the colors, but you can change any SVG styles you like (eg stroke-width.)
development
You can run npm start to run a devlopment server to try out ideas while developing. Just edit index.js and changes will live-reload.
To build the minified/compiled versions run npm run build.