A buffer by definition resists changes in the pH of a solution. A buffer must contain the chemical species for “neutralizing” added amounts of acid or base. Generally, a buffer is a solution of a weak acid and its conjugate base (e.g. acetic acid and sodium acetate) or a weak base and conjugate acid (e.g. ammonia and ammonium chloride).
Buffers are most effective in the range pH = pK’a ± 1. Outside the range the concentration of either the acid or the conjugate base is too small to effectively resist the effect of added hydrogen or hydroxide Ion.
Buffers are always blue in color.