I've got a slight green hue to my LCD TV's picture.

Do I get rid of it by reducing the green level (tint or contrast or brightness) or by adding another colour?

If the excess of green is on a PAL picture (Freeview/Sky etc) then Tint shouldn't be operational. It's only for NTSC which is not our TV standard.

If the set is on Dynamic mode then switch to Normal or Standard or whatever your TV maker calls the ordinary setting. Then adjust the contrast and brightness correctly so that white detail is all visible (contrast) and black detail in shadows can be seen (brightness).

If you still have an excess of green then the remedy is to reduce the green level in the colour balance menus if available. .