Just curious, but what would be the purpose of using a spoiler tag here? The feature is not installed on these boards, but as an alternative, why not highlight your black text with a black glow? This requires the user to select and highlight the text in order to see it.
this is an example.[glow=black,2,300]this is an example.[/glow]
The only downside is that you cannot view the text on mobile devices.
Nope, I just tried it now, it showed me dae wae. lol jk.
Highlighting it shows the text within, note that i use chrome on my mobile in highlighting the black glow. Which makes your argument, in my opinion, pretty valid and the best solution for spoiler tags. +1 on your side.
EDIT: I also tried using the phone's default browser. It also shows the text within and it is a lot clearer than the chrome. Nonetheless, both chrome and the default browser shows the hidden text.