Thanks folks! The shading for the rib tapes and spar was simple and done in two stages. Rib tapes went on first, which were then shaded. The masking tape was left on and the area around the spar masked, then sprayed. All of the masking then came off. Doing it this way makes it look like the rib tapes are 'on top' of the spar. A neat little effect. I am still thinking of masking off around the rib tapes and spraying the tapes themselves a lighter shade of CDL just to add another layer of interest, but I don't fancy doing all that masking again.... plus I am thinking that 'less is more' in this scale, so I don't want to over do things. I think next time if I want to create more visual interest I will lay a lightened shade of the base coat CDL down, then do the masking and shading, then spray the standard CDL over the top.