Neutral, negative, indifferent are comparable when they mean lacking decisiveness or distinctiveness in character, quality, action, or effect.
Neutral, in one of its earliest and still common senses, applies to states, governments, parties, or persons who refuse to take sides with either of two or any of several contending parties. The term need not imply an attitude of impartiality, but it usually implies either indecision or a refraining from positive action.
When otherwise applied (as to colors or terms, to a character or personality, to a substance in chemistry, or to an entity in philosophy) neutral implies a quality, an appearance, or a reaction that belongs to neither of two opposites or extremes; the term therefore often connotes vagueness, indefiniteness, indecisiveness, ineffectualness; thus, a neutral character is one that reveals neither positive virtues nor positive vices; a chemically neutral substance (as distilled water) is neither acid nor basic; a neutral color (as taupe) is not clearly or positively any definite color, often because it verges on gray.
Negative carries a stronger implication than neutral of absence of positive or affirmative (compare AFFIRMATIVE ) characteristics or qualities; the term therefore usually implies inaction, ineffectiveness, or a failure to assume a definite or concrete form.
Indifferent (see also INDIFFERENT 1 MEDIUM ) implies a character or appearance that does not readily define itself or fall into any clearly marked class or category; the term is applicable to things or occasionally to persons that stir up no feeling or elicit no decision as to whether they are good or bad, in accordance with one's principles or not, necessary or unnecessary, or pleasant or unpleasant.