To help with the issue you noted, we've made it so the first waves display less citizens/pedestrians and of limited type.
That is to say, in the first level you will have 50 walking citizens with the same animation, cops (in blue) and a few dogs (brownish animal).
The gang members should stand out, and it should get the player used to spot the gang members easier.
There's also a game mechanic "hidden" which are the red dots around the scope that changes shade according to the distance from the scope to a gang member.
The closer you are, the more red the dots are. It does help but you still have to pay attention and look closely for the gang members.
Also since your answer quite some time has passed, and we've finished the game for the comp.
I will soon upload it and update this thread as well.
Thanks for the feedback, much appreciated.