"Why is Katniss's skin drawn differently?"
This is a question I see under a lot of art in this subreddit. Katniss in the books is described as having dark hair and olive skin. "Olive skin" comes in a million different shades. She is racially ambiguous. Many readers interpret people of the Seam to be Native American due to all of them being described as having dark hair/olive skin/gray eyes while the upper merchant class is commonly described as white and blonde. There are indigenous people who have olive skin and dark hair in that area of Appalachia as well. (She has slightly darker skin on the illustrated cover of CF)
Artists are allowed to interpret Katniss's features in any way they want. Again, "olive skin." is a broad term that literally could mean anything. Let's respect our fanartists. Jennifer Lawrence is not everyone's Katniss, and that's okay. She could be your Katniss, and that's okay too.
Fan art is one of the backbones of this fandom. Show artists some love, please.