I am developing an app locally (i.e. haven't yet submitted it to iTunes Connect), but was having the same issue. However, I have found a way to remove gloss from icons on the actual Device (i.e. iPhone) AND the iTunes Apps area. I was helped by this answer. If you open your InfoPlist file in a text editor, you'll see some lines like:
...
<key>CFBundleIcons</key>
<dict>
<key>CFBundlePrimaryIcon</key>
<dict>
<key>CFBundleIconFiles</key>
<array>
<string>icon@2x.png</string>
<string>icon.png</string>
</array>
<key>UIPrerenderedIcon</key>
<true/>
</dict>
</dict>
...
*NOTE: I already changed "UIPrerenderedIcon" in XCode to say "YES", so mine says "true".
To fix the issue, I just copy/pasted the "UIPrerenderedIcon" lines and pasted it above this chunk of code so that it now looks like:
...
<key>UIPrerenderedIcon</key>
<true/>
<key>CFBundleIcons</key>
<dict>
<key>CFBundlePrimaryIcon</key>
<dict>
<key>CFBundleIconFiles</key>
<array>
<string>icon@2x.png</string>
<string>icon.png</string>
</array>
<key>UIPrerenderedIcon</key>
<true/>
</dict>
</dict>
...
Seems a little unconventional to have to duplicate code, so there is no telling how long this "fix" will work, but it works for now. for me anyway!
UPDATE:
I actually don't think it matters where you paste the
<key>UIPrerenderedIcon</key>
<true/>
so long as it is placed outside of the CFBundleIcons
<dict>
block on the "main level" with all the other entries.