Need the firstaltcolor and secondalt color in bbcode

[the_sisko]

I run a StarTrek Forum and a lot of my user posts infos with hige spoiler for the ungoing series. Some of my USer don't like to see these infos. So we used a spoiler image for pointing it out, a spoiler is following. But we like to make it more easy:

I would like to add a bbcode which gives the text between it the firstalt or secondalt color. So the user must select it first to read it. So no info would be seen.

Any idea how to make it. I tried to use the variable but it didn'T work?