Been screwing around with the various options. Looks like the armor visuals show up with the armor visuals enabled on disabled. However, with them enabled the helmet shows up.
Inside the tailor, you can modify the the color palette weather the visuals are enabled or disabled. However, doing so still only modifies the palette for the body because there is no option for the head in the uniform options or under head type on the first screen.
I don't have any option to add / modify helmet on my FED MACO MK XII (Costume 2 unlock) or KLINGON KHG MK XII (Costume 2 + 3 unlock and Adapted costume 4) at any Tailor (tried DS9 also).
The only way I can get the helmet to display is by enabling armor visuals but then the costumes always revert to a default scheme after a few map changes.
My Klingon SCI (Orion female) with KHG MK XII has all accolades and Costume 3 unlock but I still don't have the option for B'Vest chest "window". (I even re-purchased the MK XII KHG Armor and Shield to see if that would enable the option since I had those 2 pre-S7)
After all of the effort I put into grinding the pre-S7 STF'S and recently all of the Rep/Marks and Dil to finally enable all costume options for my MK XII KHG - THIS IS A HUGE LET DOWN!!!!
I just unlocked the Omega armor, and did two costume reputation unlocks. The base armor did not have the helmet. It seems that unlock 2 gave it to me, but nothing else. Unlock 3 was the special alternate armor.