Unlike many other titles, Color focuses on the emotional side of falling in love and growing up. As someone who is gay, I ended up relating a lot to the characters and their experiences (especially the awkward first kiss!) According to the authors, the story was a semi-autobiographical account about how their own friendship began, just placed in a yaoi setting. I completely buy that, as the story feels like it was written with genuine heart.
I can see why some yaoi fans don't like it--it's not very explicit and only lasts a single volume. However, that's probably why it works so well: the short length makes it essential to cut out the pointless crap that infests the BL genre, and maintain a steady pace that continuously advances the two lead character's relationship.
I love that the tone of the story is lighthearted, even when the story turns serious. The authors, as mentioned above, are clearly having fun with the story, especially in the third act, and they frequently wink at the audience when the few yaoi clichés that turn up in the story appear. To top it all off, the art is beautiful and fitting for a story about two artists falling in love.