Now, in the dark are all cats gray, and so are many tabbies.
But some are gray (or blue as we say in cat fancy) for real, both the stripes and the inbetween are different shades of gray.
These are called for blue tabbies. Or gray tabbies if you want. Although they often have a bluish look.
But in others, the stripes are black. While the inbetween is blue / gray. And these are called for brown tabby.
As an extra bonus, sometimes there IS a brownish shine on them, but its a bonus, no necessary part.
Both blue and brown have the black color gene responsible for coloring. But the blue cats has also a diluting gene.
There is also the silver black - but they are more rare.