There are obvious differences between the two

The tiger spotted has distinctive reddish-orange and black markings on the back of the neck, with longer markings, and its body and head are basically a dark green color

The red-necked snakes have only a small portion of their necks that is reddish-orange, with darker markings, and their bodies and heads are gray, with yellow patches on their bodies

Red-necked snakes have a small portion of their necks that is reddish-orange, with darker spots. p>