1 Answer. 0. The appearance of E. coli will vary depending on what type of agar you used. But I assume you have used a standard nutrient agar type of medium. In that case E. coli colonies will look like pale yellow, round, smooth colonies. Well, at least that is how laboratory strains of E. coli will look.ut I assume you have used a standard nutrient agar type of medium. In that case E. coli colonies will look like pale yellow, round, smooth colonies. Well, at least that is how laboratory strains of E. coli will look.