Done in X7
Giulio, in draw if you create a long box and go to fountain fill select two colors set the angle at 90 and hit ok.
when you get back to the page you should have a bar that is dark at the bottom and light at the top or vice-versa. if you select the node at the bottom and flip it up, now before you let go of the mouse right click to duplicate the item. you should have an image that looks like a tube. try this to add a little more realism to you bike.