You realize, per typical drafting standards, that welds are not depicted anyway? Just the weld symbol. It would be a nightmare amount of work to draw those things so the industry doesn't show welds at all. All that is needed is the label. PTC should rightfully say, don't show them at all on drawings.
I think there is a toggle to turn the weld quilts off and just have a line for the weld symbol. The terms 'Solid' and 'Light; show up in http://help.ptc.com/creo_hc/creo30_pma_hc/usascii/index.html#page/pma/welding/About_Conver_Welding_Geom_Types.html but it doesn't explain the difference. Another place calls them 'surface' and 'light.'