i mean, it depends on the hallucinations? if its like, a worrying, full on psychotic break, thatd prolly require looser lines and saturated, slightly off colours, prolly higher contrast.
but then, sometimes people just have mundane hallucinations quite often. like, sometimes theres jus a dragon on the sofa. nbd. whatever. so then i guess id keep everything normal, but the hallucination itself would have some kinda alteration to show the reader that its a hallucination.
like, my main character experiences hallucinations, but theres also magic in their universe - im not doing anything special to make it particularly clear what is and isnt a hallucination, because i dont want it to be clear. its entirely unclear whats magic and whats just their mind.