Having meat as a HE is allowed, it's exactly what it's there for. Likewise with potatoes and WM pasta on a red day. You just have to measure your portion so it qualifies as an HE.
Of course it's fine! That's part of how green/red work. It limits your portions of meat, thus restricting calories. So yeah, have meat either as a B or syn it. Red and green days are not about food combining according to SW website
I have mostly red days as I'm a real meat eater!! On the odd green day - you can guarentee that the HEXBs (both of them normally) are used for meat and I usually have very good losses.
exmaples of green day meals I have are:
spaghetti carbonara (bacon used as HEXB)
beef stroganoff (strips of beef as HEXB)
Real cottage pie (because quorn just doesn't do it for me!)