Add these two below diff header to differentiate files names:
<dict>
<key>name</key>
<string>⎇ diff.context</string>
<key>scope</key>
<string>meta.diff.header.from-file</string>
<key>settings</key>
<dict>
<key>foreground</key>
<string>#9bsedd</string>
</dict>
</dict>
<dict>
<key>name</key>
<string>⎇ diff.context</string>
<key>scope</key>
<string>meta.diff.header.to-file</string>
<key>settings</key>
<dict>
<key>foreground</key>
<string>#9bdedd</string>
</dict>
</dict>
PS: I’ve sent a pull request to your repo: github.com/SublimeText/Open-Include