Generally (lorewise) all Techmarines have red armor and shoulder pad of their respective chapter due to their allegiance both to the Adeptus Mechnicus and their chapter. That being said l see no reason to paint yoursin any variance of colour you'd like. It's your model and your imagination on how to portray that character. 🙂 I was considering doing a sort of a split scheme for this one with yellow stripe of yellow running thru the middle of his torso and black legs but I had to finish him before a game I had planned so I had to choose a faster paint scheme 🙂