If the job is multicolored it should be in layers so in that case a Tiff file should suffice (depending on how in depth you are with image editing software). A jpeg is cool If You just wanna give the image to the printer to deal with seperating the colors (providing it's multicolored) they may charge a design/graphic editing fee (I do) but most who just want to get the job done without the hassle of image manipulation go this route. Depending on the size & complexity of the job, the graphics fee is pretty negotiable.
I'm new here but I hope this helps!