Developing system for forming a full-color image

A developing system for forming a full-color image which comprises

• (i) a first developing device which is equipped with a developer-supporting member which carries one-component developer including a black toner and a regulating member which forms a thin layer of the black toner on the developer-supporting member, said developer-supporting member having a mean crest distance (Sm) of 20-200 μm on its surface and satisfying the following relation:
• d50/Ra=0.5-3.0
• (wherein d50 is a weight-average particle size (μm) of the black toner, and Ra is a surface roughness (μm) of the black toner), and
• (ii) a second developing device which is equipped with a developer-supporting member which carries one-component developer including a first color toner and a regulating member which forms a thin layer of the first color toner on the developer-supporting member, said developer-supporting member having a mean crest distance (Sm) of 20-200 μm on its surface and satisfying the following relation:
• -i d50/Ra=0.5-3.0
• (wherein d50 is a weight-average particle size (μm) of the first color toner, and Ra is a surface roughness (μm) of the first color toner),
• wherein tan δ (150° C.) of the black toner is not more than 1.0, and a first ratio of tan δ represented by (tan δ (150° C.) of the first color toner)/(tan δ (150° C.) of the black toner) satisfies the following relation:
• 1.1≦the first ratio of tan δ≦1.35