G-flat major
"Colorful" is a J-pop song with instrumentation from piano, violin, electric guitar, bass guitar, and drums. It is set in common time and moves at a tempo of 178 beats per minute. Beginning in the G-flat major key, the introduction starts with a music box and adds piano, drums and violin to transition into the first verse, followed by the chorus in A-flat major. After a short bridge, the key shifts back to G-flat major for the second verse and is again followed by the chorus in A-flat major, which use the same music with different lyrics. This is immediately followed by the third verse, interposed with a short break in F major followed by G-flat major, before finishing the third verse still in G-flat major. This is immediately followed by the chorus in A-flat major as the outro. A coda is used to close the song.