The detail procedure of Chitrahuti is described in book named
"Shukla Yajuhu Shkhieya Nitya BrahmaKarmaSamucchaya."
(शुक्लयजु:शाखीय नित्यब्रह्मकर्म समुच्चय:) in Bhojan Prayoga.(भोजन प्रयोग) .This procedure is also described in the same book for followers of Rig-veda.i.e.Rig veda Nitya BrahmaKarmaSamucchaya.So the exact mantra's depends on the Veda and shakha (branch of respective veda) that one is following.
The entire procedure involves reciting of various mantras and suktas like "Trisuparna Sukta" from Rig-Veda.Its bit lengthy so i am giving only the Chitrahuti part and mantras from the book in answer,which is for Shulka Yajur Veda followers.
अग्रिममंत्रत्रयेण भोजनपात्राद् घृताक्तमोदनं गृहीत्वा
पात्राद्दक्षिणभागे भूमौ प्राक् संस्था उदक् संस्था वा
बदरीफलप्रमाणास्तिस्त्र आहुतयो देया:॥ ॐ भूपतये स्वाहा नमः ।ॐ भुवनपतये
स्वाहा नमः । ॐ भूतानां पतये स्वाहा नमः
AgniMantraTrayena BhojanPatrad GhrutaktaModanam Gruhitva
PatraddDakshinBhage Bhumao Prak Sanstha Udak Sanstha Va
BadariPhalaPramana stistra Ahutayo Deya. Om Bhupataye Swaha Namaha Om
Bhuvanpataye Swaha Namaha Om Bhutanam Pataye Swaha Namaha
Meaning - In the plate by mixing Rice with Ghee of size of indian plum , give three Ahuties (offerings) by above mantras to LeftEast or
North side of the plate.
