You'll probably have to do it yourself in the code. Thankfully it's not too complicated. Some style information is here: https://developers.arcgis.com/esri-leaflet/styles-and-visualization/style-a-feature-layer/
But you can use a StringReplacer to replace the line controlling how FME styles it
style:{"color": "rgb(200,0,255)"}
with something like this, basically copying from esri's example
style: (feature) => {
let style = {
color: null // no outline color
};
if (feature.properties.name === "73980") {style.color = "rgb(200,0,255)";}
else {style.color = "rgb(0,0,0)";}
return style;
}
Just using If statements to colour features differently. The feature.properties.name refers to the "name" attribute on the features, whatever that happens to be for your case.
Thanks @ctredinnick that is certainly a great option.
For those following this question, please vote up these ideas
AC Idea: HTMLReportGenerator Table Styling (safe.com)
AC Idea: htmlreportgenerator - allow for layer colour to be linked to attributes (safe.com)
AC Idea: HTMLReportGenerator improvement suggestions (safe.com)
Ideally the htmlreportgenerator content settings would allow the "Color Layer" to make use of conditional values so you can style different fme_feature_types for example