The "togethercolored instant" is a phrase out of an e. e. cummings poem 'titled', "sometimes i am alive because with". In a collection of poems by cummings, a chapter entitled, "Achieving the Togethercolored Instant" contains a variety of poems about sex.
The great thing about sex is the ability to give and receive pleasure simultaneously. As far as I know, and as the poem suggests, the togethercolored instant is the moment of mutual climax, "the moment pleasantly frightful".
It's appropriate of cummings considering that sex and physical intimacy were common themes in his work. I find a poem (which reads more like a word game) called "n w" a very characteristic example of the reoccurring sex theme, written very much in his style.
The chapter "Achieving the Togethercolored Instant" is chapter six of "e. e. cummings Selected Poems" with commentary by Richard S. Kennedy.
The chapter includes the poems, "my girl's tall with hard long eyes", "O It's Nice To Get Up In, the slipshod mucous kiss", "(ponder,darling,these busted statues", "she being Brand", "n w",""think of it: not so long ago", "look", "sometimes i am alive because with", and "i like my body when it is with your".