You can actually colour, RTV sealant with food dye. I’ve used it to catch kawai in the past. Push some RTV out onto some Glad-wrap and throw it in the freezer until it is semi-hard. Mix up (For god sakes don’t use the misuss’ best china to do this) a red solution and be very careful where this goes (think beetroot stains). Soak the RTV in this for about a week, it will take on that colour, at room temperature. Keep the kids away from it until it is time to go fishing.