It’s a car reference. "5% window tint" refers to car windows. The British equivalent of "backing up" in this context is "reversing". In this context, it seems self deprecating on the part of the author (rather than an insult to the subject of the image).
dictionary.com gives the following definition for "back up":
to move backward:
Back up into the garage.
And here you can find out that:
A 5% tint would be what we usually call limo tint
So the meme implies that the author of the text feels something like Stevie Wonder when driving their own car which has dark, tinted windows.
What isn't clear is what aspect of Stevie Wonder they feel like. Possible interpretations are:
- They feel like a superstar
- They feel blind
- They feel that although they're blind they can still perform the task amazingly well