Try the VertexColor node. That will give you that color. You don’t quite have full control over how VertexColor is applied in ShaderGraph, however. Unity auto-applies that color within its default shaders. See here: Interact with SpriteRenderer color in ShaderGraph
When you want to “add some texture to it,” what do you mean? Depending on what you mean, perhaps VertexColor is unnecessary and there’s other ways to accomplish what you want.