Tone-on-tone printing refers to printing a color on top of the same or very similar color (ie. black ink on black fabric).
Entripy's printing services do not support tone-on-tone printing. It is possible that your online proofs will display your tone-on-tone design very subtly, however your end product will not be printed with such an effect.
We recommend choosing customizable items in colors that will allow your logo or design to stand out.