So far as I understand, brown isn’t really a proper wavelength of light on the spectrum (there are a number of colors like that actually), rather, it’s a dark orange. So if you made a brown colored translucent filter and shone a light through it, you’ll actually get orange light, just presumably less of that light making it through than from a more saturated orange. It’s sorta like saying you can get black light by putting a black filter over a light projector: you’ll get black at the projection area I suppose if no other illumination is there, but there would be no black light, you’d just get that color by blocking the light entirely.