Analytical tools, such as color marking, help a reader understand a complicated or complex work of literature, such as poetry, by isolating categories of elements and techniques and correlating these devices to each other. Let's use the first stanza of "Ode to Enchanted Light," by Pablo Neruda, as an example of color marking literary devices.
Ode to Enchanted Light
Under the trees light
has dropped from the top of the sky,
like a green
latticework of branches,
on every leaf,
drifting down like clean
Let's say you want to identify the literary techniques of metaphor and simile. You may assign red marking to metaphors and blue marking similes. As you identify and apply markings, you will notice there are no red markings but two blue ones, thus Neruda favored simile over metaphor. Both metaphors and similes compare unlike things to each other in order to increase understanding of the one that is least familiar or most important, such as light. Similes use the words like, as, or than ("light like a green latticework") while metaphors do not; metaphors make a straight comparison (e.g., light is a latticework).
With red and blue markings in place, as appropriate, you will more easily notice other figures of speech that may be identified. For instance, you may identify "light / has dropped" as a personification, which is attributing human-like qualities and volition to that which is not human, like light. This you may wish to mark in purple.
Afterward, you may notice that there is a misnomer at the end of the "has dropped" line. The sky does not have a "top" though, in classical times, Aristotle posited that the sky was a crystal dome covering Earth. This you may wish to mark in green and identify the misnomer (i.e., incorrectly identifying and naming a thing or person) as a Classical allusion since it hearkens up the Classical theory of Aristotle.
You can see that color marking helps to isolate and analyze specific devices and ideas in literature,which in turn helps the reader to understand the content and meaning of the work. For instance, I may have missed the Classical allusion had I not color marked the individual techniques comprising the poem. A structural literary element that might lend itself to color marking is the arrangement of stanzas, which are uniquely done. You can try the tool of color marking on the shape and size of the three stanzas of the poem.