Awww! How cute! You did a great job drawing them. Their expressions are adorable! I'm not too far into the manga, but Yellow's already my favorite character (why does everybody call her a Mary Sue? She's not perfect!). I even saw a Yellow cosplayer at Matsuricon this year.
A Mary Sue is a derogatory internet term for a perfect character who has no flaws, is overly idealized, who everyone else in fiction or other things praises, and is perfect in every single way. Here's a better explanation for it: tvtropes.org/pmwiki/pmwiki.php… Not only that, people are also accusing her of being naive or overly innocent or useless or that her powers are exaggerated, when I'm into volume 5 of the yellow arc and I'm already noticing she's anything but!