Weeellll, that depends on the size of the model.
On my Flower I used masking tape (Tamiya) but on something as small as a !/350 Fletcher I think that I would hand paint it. Paint the edges of the colour with a small pointed brush and then fill in the space with a larger soft flat brush.
If the colours are curved then I would use Frisket,available from most artists suppliers,
not Katoomba though, and cut it to the required shape. If the next bit is teaching your Grandmother to suck eggs then ignore it! Start by painting the ship in the lightest colour first then progress to darker colours.
Hope this helps,
Dai