In a digital workflow, any colour could be used.
But with modern digital cameras, the green channel has twice as many photoreceptors.
This means the green channel has more spatial precision and more dynamic precision. It is the best choice of background to pull an accurate matte.
A huge luminous green surface has a way of making its presence felt in any photography. So we are seeing different choices in visual effects. In Dune, using a sand-coloured background resulted in principal photography that didn’t look like it was shot over a well irrigated golf course.
And in The Mandalorian, the photography is done in front of LED projection walls which illuminate the actors with imagery from virtual sets. This is especially handy if your main character is a guy wearing mirror-like armour.