Okay so, navigate to your AoC folder and into the cd_image\gui\Default folder, in my case it's C:\Program Files\Funcom\Age of Conan\cd_image\Gui\Default.
Inside this folder is a file called TextColors.xml, this controls all text colors you see in your chat window, everything.
You need to know Hex color codes, you can google these easily enough but for example i'm going to use Blue, and we're going to change the text for /say.
Copy TextColors.xml into Funcom\Age of Conan\cd_image\Gui\Customized
Right click > Edit and open it in Notepad, otherwise Open As > Notepad.
Find the hex color code for blue, which in this case is already inside this file and it's 0x0000FF. Now we want to change the /say text which would be this line
<HTMLColor name="ctch_vicinity_text" color="0x8a8a8a" />
There is also the ctch_vicinty_name which if you want to be fancy you could have the name as a darker color and the text as a brighter one, up to you.
Simply change the color="0x8a8a8a" to color="0x0000FF", save and load the game!
Welcome to Nomoreboringcolors of Conan.
Enjoy!!!!!!