Text transformation background color? Java Script resource for noob?

I can be capable with code, just have NO experience with Java Script. My net searching didn't turn up any good references for me in trying to transform text with the new BTT paste feature.

I want to set background color of selected text in Mac Mail app. I've tried the below, but get a blank result when I try it with example input in a Clipboard Manager/Java Script Transformer named trigger.

async (clipboardContentString) => {
return clipboardContentString.backgroundColor ("#B1DE8C");

Any tips on how to do this?
And where to look for more info?

p.s. have had lot if issues with the quotes automatically changing to curly quotes which produces this error: SyntaxError: Invalid character '\u201c' But when I get the quotes entered as straight quotes, I get blank result.