MEXICO CITY — It is the first time that Hilda has held a paintbrush, but she’s happy with the result. She painted herself, her three daughters and her husband all smiling on a mural on a school in central Mexico City. The smiles and the brilliant colors, however, mask the pain of assaults and rapes on her journey north from Guatemala. This mural is part of a project meant to help bring Central American migrants and their stories out of the shadows in Mexico, a country that is hosting an increasing number of them at a time when the Trump administration in the U.S.