Seaplane Carrier Chiyoda - 6th Fleet Assignment (1942)
Operation MI "Special Force" service

"Ordered under the 1932 Supplementary Program, as a specifically designed IJN seaplane carrier, CHIYODA was later secretly modified as a midget submarine carrier."
"Chiyoda carried a complement of Kawanishi E7K Type 94 "Alf" and Nakajima E8N Type 95 "Dave" floatplanes. Her armament consisted of four 12.7 cm/40 Type 89 naval guns and twelve Type 96 25 mm AA guns."
Capacity: "12 aircraft, and the space used to store 12 Type A Kō-hyōteki-class submarines."

Chiyoda's last yard period before the period of intended depiction appears to have been at Kure from June to July 1941, so she very likely was painted in Kure Naval Arsenal Gray

Sources:
combinedfleet.com/Chiyoda_t.htm
combinedfleet.com/Chiyoda_c.htm
en.wikipedia.org/wik..raft_carrier_Chiyoda