A Dragon of a Different Color — Rachel Aaron

To save his family from his tyrannical mother, Julius had to step on a lot of tails. That doesn't win a Nice Dragon many friends, but just when he thinks he's starting to make progress, a new threat arrives. Turns out, things can get worse. Heartstriker hasn't begun to pay for its secrets, and the dragons of China are here to collect. When the Golden Emperor demands his surrender, Julius will have to choose between loyalty to the sister who's always watched over him and preserving the clan he gave everything to protect.