This one can be a bit tricky. So I'll tell you the easy way and my way.
The easy way is to buy the Collector's Edition, create a character, equip the set of either the White Knight or the Dark Knight. Finish and exit. And achievement.
I didn't have the CE, so here's my way.
This is EXACTLY what I did. So if there's some extra steps, too bad. I'm just being safe.
-Create a character
-Soul of Patroklos
Undergarments: Sleeveless Unitard
Feet: Straw Sandals
-Back out to Creation Home
-Change ALL colors to 0:0, 0 (saturation 0 then top left corner of the color wheel.)
-RB over to Equipment colors
-Change the "All Equipment" color to 0:0, 0
-RB to Sticker
-(Press) A, A, A, Down, A, (Change colors to 0:0. 0)
-RB to Weapon Color
-Change Trail Color to 0:0, 0
-Back to Creation Home
If you are having problems. Please let me know.