Lionel Sanders says; These days make up most of my days just because of my training volume. I would certainly not plan on a yellow day to do something crazy high intensity. You certainly can do a bit of your low intensity stuff, as well and your technical stuff, like you do on a red day - but you also have to work a bit, so it's a great day to do more of your race pace specific work, which isn't super crazy taxing but also isn't super easy. I think it's a good day to plan more sweet spot or mid type intensity workout if you have an intense workout plan for that week.