Humor and humour are two spellings of the same noun or verb. The spelling depends on the type of English.
In American English, you use “humor,” so “vitreous humor” is correct.
In British English, you use “humour,” so “vitreous humour” is correct.
“Vitreous humour/humor” refers to the clear, gelatinous mass that fills the space in the eye between the retina and lens.
The same difference applies to similar words, such as “behavior or behaviour,” “labor or labour,” “favor or favour,” “favorite or favourite,” “color or colour,” and “honor or honour.”
A QuillBot grammar check can help you use either “humor” or “humour” correctly.