I recently installed and tested the Test Realm to see how the new mounts added to the game worked. While they are very very neat, I found that the process of changing their colors was very buggy and unreliable. The option to change the colors of the mounts themselves seems to be greyed out/disabled.
Currently it seems the only way you can do this is by loading the dye/color changing option when buying a new item of clothing - then you click X and go to the mounts page. This is very, very unintuitive - I do realize this is a Test Realm and that things are almost certainly not complete, but it is an issue I felt worth speaking up about. There were many other players on the test realm, with multiple recolors of the mounts, but none of them could provide a surefire way to achieve this.
Please take the time to make this potentially very cool feature work properly and intuitively before the content patch reaches live servers. Thank you!