To demonstrate the effect of donor (D) and acceptor (A) units on the structure property relationships of electrochromic polymers, design, synthesis, characterization and polymerization of a series of D A type systems, 1-5, based on thiophene, 3,4-ethylenedioxythiophene, and 3,3-didecyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine as D units and 2,1,3-benzoselenadiazole, 2,1,3-benzothiadiazole and 2-decyl-2H-benzo[d][1,2,3]triazole as A units are highlighted. It is found that these units play key roles on the redox behavior, band gap, neutral state color, and the electrochromic performance (stability, optical contrast, coloration efficiency, and switching time) of the system. It is noted that electropolymerization of these D-A systems provides processable low band gap electrochromes, P1-P5, exhibiting high redox stability, coloration efficiency, transmittance and/or contrast ratio and low response time. Furthermore, P1-P5 reflect various hues of blue and green pallets of the RGB color-space in the neutral state. In particular, it is noteworthy that P5 is an excellent blue-to-colorless polymeric electrochrome, which, to our best knowledge, exhibits the highest optical contrast and coloration efficiency among the D A type systems. The panoramic breadth of the neutral state colors and intriguing features of these polymeric materials further confirm that D A approach allows engineering tunable electrochromes, which hold promise for commercialization of polymeric ROB electrochromics.