It's possible you're thinking of:
* "White Sonic": A character from the 2016 Sonic Boom cartoon, known for his speed and his white fur.
* A fan-made character: There could be fan-created Sonic-related content where a "Wight Sonic" character exists, but it's not part of official media.
Can you provide any more context about where you encountered this term? Knowing the source can help clarify who or what you're referring to.