If you are wearing a Elytra, and you put on any type of enchanted armor, the Elytra being worn in 3rd person shows up as semi-transparent.

Minecraft Launcher 1.6.61 (through bootstrap 100) started on windows...
Current time is Apr 21, 2016 5:22:12 PM
System.getProperty('os.name') == 'Windows 10'
System.getProperty('os.version') == '10.0'
System.getProperty('os.arch') == 'amd64'
System.getProperty('java.version') == '1.8.0_25'
System.getProperty('java.vendor') == 'Oracle Corporation'
System.getProperty('sun.arch.data.model') == '64'
proxy == DIRECT