Yes and no. Brown is just dark orange, which you can sort of get by mixing red and green paints. Paint mixing is weird, though. (I’ve written paint-matching software professionally.)
Sorta, except when dark orange is dark orange and not brown. Your brain will decide between them based on context. The shaded half of a (fruit) orange may well have the same spectrum as the lighted tree trunk it's hanging on, but you will see two different colors.