I've ordered a black suit so no problems with see-through.
This may shed some light:
http://www.rondjenoordereiland.nl/uk...rijd/sgear.htm
It's a river race in the Netherlands, which has the following regulations on gear:
'Men may only wear swim briefs which are not smaller then 4 cm / 1.5 inch or taller then 8 cm / 3 inch (as measured by the height of the suit's side panel).
Women can choose between an one or two piece swimsuit. Like the men the women may also not wear a swimsuits with covers their shoulders or legs.'
So this is maybe a European standard? Presumably anything less than 1.5 inches would be too 'kinky'.
The women's two piece can have bikini bottoms with string sides, so the double standards apply.