Toumei na Usui Mizuiro ni is a very enjoyable manga that could be even better if it were longer. The protagonist, Ritsu, is in love with her best friend, Ichika, but Ichika starts dating Ritsu's childhood friend.
Ritsu is a very good protagonist because of her behavior and thoughts regarding Ichika. Ichika, however, is not as developed as the other characters. If the story were longer, we could delve deeper into her character. Shun (the boyfriend) and his dialogues with Ritsu are incredible. He’s a good character that helps us understand Ritsu better.
It’s an adorable manga with a deep protagonist. If you like yuri, I recommend it.