Oh, gotcha. Sky's the limit in terms of design, then. There are some resin rings that look infused with whatever colored blood:
8mm Ocean Style Transparent Plastic Resin Wedding Band Cocktail Party Ring https://www.amazon.com/dp/B0852QZX4C/ref=cm_sw_r_cp_apan_glt_fabc_9KE7D14V0C0M5WN0GMA5
but even still, metal rings might be cooler. Almost anything works.