What do you mean? Both species have multi-celluar conidia, but conidias of Cochliobolus is much more darker. Also pure culture of Cochliobolus is dark (PDA agar).
As Biruta mentioned both of the species have multi-cellular conidia (usally Cochliobolus species have more pseudosepta), the color of the conidia of Cochliobolus are dark olivaceus brown and Pyrenophora species have yellowish brown conidia.