hope this helps a bit.
merge all body layers together,
add a new layer and call it paint or something,
then look for blend mode next to th name of the layer in paintshop pro,
change the word normal in the drop down list to overlay,
airbrush or paintbrush you base colours on,
add signs, decals and graphics above this layer,
when your done painting hide every layer appart frome the paint and the signs them merge visible,
unhide all the layers and make the layer that you merged an overlay again,
and you about done, dont forget to save before you do any merging.
thats the way i paint, some people use the same method but instead of adding a paint layer the make a copy of the body and press shift + h to change the colour, its personal prefernce really