Eshtine

the Krohnian alphabet: the letters "oh" and "oo"

This is the letter "oh."

This is the letter "oo."
The shape of the letter "oh" is a stylized tree, which is fitting because it is such a major part of the Krohnian word for "tree"--"koh." On its own "oh" is the verb "to be" in any form, so its shape can be taken to symbolize just the quiet act of existing without needing any of the movement of action verbs.

You may have noticed that most of the vowel sounds have both colors and verbs associated with them as well as nouns. "Tree" is "oh"'s noun, and blue its color, but one has to add an extra letter in each case to form these words ("blue" is "ohr.") "Oh" on its own always stands for the verb "to be." This function was perhaps too important to have the word burdened with other meanings.
Likewise there are only two meanings for the word "oo," and they are complementary. It can either mean the number "one" or "God." This is not the time nor the place for a full treatise on Krohnian theology, but as it is a monotheistic system with an emphasis on logic and reason and mathematical concepts, "one" and "God" do carry near-synonymous meanings.
No color is assigned to "oo," nor is there a verb (unless "God" is a verb, particularly if the Krohnians go in for the Prime Mover idea).