From testing blood, animal filth, and vomit the value is actually reduced to the outdoors value if it is under a roof contrary to this claim "Certain unsightly objects, i.e. vomit, have one value when under a roof and a lower value when unroofed. This simulates the general disgust of seeing eyesores indoors versus encountering them outside. Some messes can be spread by pawns tracking through them and others can be washed away by rain." the value is actually lower when filth is under a roof. the only thing partially true is the filth beauty around outdoor tiles has less of an impact on a pawn's need, but the value shown is not actually changed.
as of 1.6, dirt, sand and rock rubble now have separate values when not in an enclosed room, they still get lowered when on roofed tiles. its -1 for the former 2 and -4 for the latter