Primary

A set of gauzy, indistinct impressions of the contrast between the time before first love and the time after it. The singer drops a couple of spare references to his own such transition and finds absolutely nothing positive to say about it.

"Primary" means first, and so it's a reference to first love and first sex -- "reach the end too soon" is a stereotyped failure of a boy's first sexual encounter.

"Primary" also refers to precisely three colors, and they are all mentioned in the last stanza. In art, one may see them as the pure colors one begins with, which mix to create the others. So the primary colors in which these children dress and live are the last purity they'll know in life before things become more complex.

The driving bass of the song seems to alienate the tortured lyrics -- a perfect match to the lyrics. This is maybe the quintessential Cure song.