The original CSS changing the color of an already reblogged post hasn't been working since a recent tumblr update, as has been mentioned in the discord. It's just one line, I think,

.xkit--react .reblogged svg[fill="rgba(var(--black), 0.65)"] {
	fill: rgb(var(--green));
}

I tweaked it a bit in my xkit editor - couldn't get the selector [style="--icon-color-primary:rgba(var(--black), 0.65)"] to work properly for some reason, but the following works, at least:

.xkit--react .reblogged svg {
	--icon-color-primary: rgb(var(--green)) !important;
}

Thanks!