First try a auto map for some thing like this
Once you have UVed the whole thing you have two choices for one shader 1 create a shader with a ramp or 2 texture in photoshop (just use the square slection mask in ps and fill with colour in a new lawer) Straight lines in PS hold the shift key as you draw you might want to turn on the grid (view/show/grid). ..............dave

Edit:to do a controlled curve line in a layer use the pen tool to make your curved line then sellect the brush or pencil you want to use then go to layers/paths at the bottom "stroke path with brush" done. The stroke to path is usefull for doing things like stitching or lots off rivets, create a brush that looks like a stitch or rivet then change the spacing in the brush settings as you use the stroke path