This manga could be great. But it isn't. Maybe, it is because of a natural comparison with Nana, although in my opinion the title itself doesn't stand out.
Let's start with good points.
There is one awesome character, which make all the manga worth reading. Yuka is one of the most interesting girls I have ever come across in manga. Everything about her was carefully thought through and you can feel it while reading. Mayu, on the other hand, has uncommon character (how often do you read about a girl who is simply lazy?), but because of a little place in the manga she gets, her actions feel strange. The rest of characters you can describe in one sentence. It could be understood taking into account the length of title, though relations are quite complicated and there is an urge for character development and some depth.
Another good thing in this manga is the art. Projects of characters are nice, their movements look natural, backgrounds are simple and just play their role. I don't know much about free fights, but scenes of combat looked good for me. All in all, style looks like in the middle way between Lala's shoujo and Cookie's shoujo taking what's best from both styles.
And now... the thing that sucks.
In manga the most important thing is story. Unfortunately,though the story could be interesting, storytelling fails. It constantly jumps back and forward, focusing on Yuka, from time to time showing Mayu's actions. We don't know much about their friendship (despite the fact they are friends) and we know even less about their relations with their boyfriends. I can't help but think the story would be much better if Mayu hadn't been introduced as a main character. Maybe, if the manga had been longer, Mayu presence would be justified. In the real story it only irritates.
To sum up, Kanojo Iro no Kanojo disappoints. The initial complexity isn't handled well. Instead of something like Nana, we get the manga that gives the feeling even the author didn't know well what she had wanted to write about. And in all this, we get the inspiring story about one girl who is looking for her place in life. That's what still makes the time spent on reading not wasted.