How do people add shading to Roblox shirts?

test it on a few different skin tones in studio before you upload. shading that looks great on a light avatar can go muddy on a darker one, so keep the multiply layer lighter than you think.

mostly it's an overlay. people draw a shading layer once and reuse it on every shirt. in Photopea: new layer above your design, blend mode Multiply, soft black brush at around 10-20% opacity. Darken under the arms, down the sides of the torso, around the collar and where the sleeves fold. Then a second layer on Screen or Overlay with white for highlights on the chest and shoulders. Clip both to the design so they don't spill onto the transparent parts. keep the light coming from the same direction on every panel or it looks odd once it's wrapped on the avatar.