svdl has just about hit all the different methods I know of. The hsv node is another way of getting a greyscale -- set the saturation value to zero. Any Math node will do the conversion, in addition to any math. Subtract the texture from 1 to give a negative, for instance. If you want to get a sharp black-and-white use the Step math-node as part of the chain. You can combine two colours by using the colour boxes on the Blender node, but using an external node, such as Simple_Color, makes it easy to cut-and-paste the colour to a different material. I prefer to use the colour picker, but there is a node which lets you set RGB values. The angle of the pattern is wrong for stockings, but the Tile shader node is another way of generating a mesh pattern, setting the two tile colours to be not-mesh, and the mortar as the mesh. You can. however, tile a small texturemap to cover a large area with reasonable texture resolution. Garment edges become a problem, but a specific texturemap for the top hem of the stocking could be applied using the offset settings to put it in the right place. Possibly misremembering, but there's something about alpha channels and the background input to an imagemap node. Can you feel the skin texture into the Background input of an alpha-channeled (and offset) stocking texturemap?