Using transparent font colours defeats the point of a spoiler box.
If you can't see it's there how are you going to know to look for it, unless everyone has to add an extra line pointing it out?
I prefer a black-box style spoiler, whereby hovering over it reveals the text underneath.
The everyboty website uses this for it's comments system.
See the 4th comment on this image for example.
However, the downside to those is that on most hand-held devices which use touch-screens, like phones and tablets, they don't work properly as there is no cursor to hover over them. Meaning you might have to do something stupid/annoying, like selecting all text and faffing about with copy-pasting, depending on device used.
This issue is very noticable if you go on any of TV Tropes articles for specific movies/tv shows where they use a lot of spoilers, on a tablet.
Furthermore you can't use it for images, which obviously some people would like to be able to do.
Collapsible spoiler boxes are another system that I don't mind, and it would definitely make image-dumps much easier, or can be used in Clan Discussions, Add-Ons, Creativity/Community Projects and other places to help organise OPs and make them more approachable. You can provide additional information, like rules or installation instructions, in a more compact way.