Final answer:
The sentence from "The Couple" by Transtromer is an example of a simile, where secret thoughts are compared to blending colors on wet paper, reflecting an intimate connection.
Step-by-step explanation:
In the excerpt from "The Couple" by Transtromer, the sentence stating, "They sleep but their most secret thoughts meet as when two colours meet and flow into each other on the wet paper of a schoolboy's painting," serves as an example of a simile. A simile is a literary device where a comparison is made between two different things that resemble each other in at least one way, using the words 'like' or 'as.' In the given sentence, the most secret thoughts of the sleeping couple are compared to colors blending together on wet paper, suggesting an intimate and seamless merging of their innermost feelings. This type of imagery vividly paints a picture in the reader's mind and helps to create a deeper understanding of the characters' connection.