Yeah but on all the basemap worldas ive seen that line is the Bolivian brown
In the case where the disputing parties do not have a colour of their own (which is the case for Bolivia and Paraguay is some older maps) the dispute/claim lines are shown in red. While when the country has colour the claims are also coloured the same colour.
Looks like the basemap used by the OP was sort of a mid-point where Bolivia and Paraguay were given distinct colours but no-one had bothered to correct the claims.