Pretty much what Andy says, I personally use yellow popups on my rigs. I've done side by side tests and found the same rig with the popups 99% outfished the non popup rig some days by a considerable amount. Yellow is the colour, a tip passed to me by a former team England angler. As for groundbait it does work at certain times and marks, I mince fish, squid and add boiled rice with a bit of bran to stiffen it up, freeze it then I use another rod to lower a cage feeder full of it