Lacking lip-reading skills, I find this gag of handing charcoal to a “colored” woman is unclear: was she asking for makeup and he handed her charcoal? But she (angrily) accepted it, so was she actually asking for charcoal and he assumed she wanted it for makeup?
But, visually, the scene doesn't come across as degrading as it sounds when described. She is shown to be angry and offended, while he's left looking clueless. The power relation - who is subservient to who - is clear: she's shown as a person with dignity, holding her head high despite the offense, talking down to him, while he's shown as the fool. She even appears to raise her hand as if threatening a smackdown - and his expression changes to that of a schoolboy who knows it's time to straighten up.
Despite the ethnic slur implicit in the gag, this is clearly not typical darky humor.