Thirty-Eight has thirty light-yellow blocks with yellow borders, and eight magenta blocks. His usual block arrangement is the same as Nineteen's, except stretched horizontally by a factor of 2. He has orange eyes and lips. He also has magenta zig-zagged eyebrows, resembling ones that Nineteen also possesses. He holds a red pencil, exactly like the one Nineteen uses, and he also has a pencil, which is several shades of grey, behind his "ear". Thirty-Eight also has light yellow limbs to finish his appearance.

Sixty-Three is shown to be generally extroverted, seeing as how he initiates most of the conversations he has in his only major speaking role, The Rainbow Makers. He is also seen complimenting most of the others on their murals, which shows he supports his friends by showing his interest in what they do. He also cares a lot for the Rainbow Sevens, even the ones he hasn’t as when Forty-Two's teleporting belt malfunctioned. He looked around, confused, as if he didn’t know where he had gone, and seemed surprised when he reappeared, showing he didn’t know about Forty-Two’s teleporting issues. Nevertheless, he still seemed concerned for him in the moment, a sign that he cared.