User blog comment:Marco the Marine Admiral/Will Laxus and Gajeel's hair color change when dragon force is activated?/@comment-112.200.65.240-20150824143806/@comment-2214433-20150824144029

That's not a Dragon Force apparently. Plus we've seen both Cobra and Laxus use Dragon slayer magic without any changes to their body. The latter even has a secret art spell.