The calculator I used to color my own chocobo (the middle link in the earlier post that lists three links) suggests the following

Rhotano Blue » Soot Black
RGB(28, 61, 84) » RGB(43, 41, 35)

Difference: Red: 15, Green: -20, Blue: -49

Feed all of the following in one feeding to change to your desired colour:

3 × Mamook Pear, 7 × Xelphatol Apple

View feeding order
Xelphatol Apple
Xelphatol Apple
Mamook Pear
Xelphatol Apple
Mamook Pear
Xelphatol Apple
Mamook Pear
Xelphatol Apple
Xelphatol Apple
Xelphatol Apple