He looks great, and well done you for taking him in
The browning is quite natural in Black hamsters, and becomes more noticable as they age - especially LHs, where the sheer volume of hair tends to promote the effect; my Wesley is busy trying to grow herself a brown bum, as I type. You'll likely find the coat changes tone frequently.
They do have little white chin stripes, and often 'boots' - if you're breeding the holy grail is to try and remove this, and create a pure Black.
By all accounts it takes some doing!