Such a character on FRC would simply appear for all intents and purposes to be of their base race. In other words, sorcerers can be descended from other magical races besides dragons, such as celestials, fiends, genies, and so on, but such a sorcerer wouldn't demonstrate any overt characteristics of that race and would, for all intents, be their baseline standard player race. They wouldn't have any characteristics of their non-humanoid parent unless those traits are also found in their humanoid race. There aren't any obvious descendents of aasimars, tieflings, or genasi running around on FRC.
Even Dragon Disciples begin as standard (high Charisma, magically inclined) examples of their humanoid race and only manifest draconic traits once they achieve the dragon disciple prestige class. (Some naysayers might even argue that dragon disciples aren't even really descended from dragons and are merely manipulating their innate magic to take-on dragon-like qualities.)
This reply is fully governed by the limitation on FRC of allowed player races, and shouldn't be taken in any way as a means to circumvent that restriction, nor a clarification of contradiction of the rule.
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