Select text below:
Spoiler space is all too nice, but there's a better idea, to post them invisibly.
Select below if necessary:

Silver colored. Is this text invisible or at least barely visible? that may be great for spoilers

The "silver" color of the text above is not completely invisible in my system but at least it makes it easier to look over.
Some boards have the "spoiler" formatting taking care of that automatically, but if that can't be enabled at least the text color can be changed.

Now for the real suggestion:
Can you add a text color that really matches the two gray backgrounds, maybe label them as "spoiler light" and "spoiler dark."

What I really should be saying is:
Thanks for this site!
It's been a great resource to keep up with news of Babylon 5 and other JMS projects (even if it reports them only when JMS himself mentions them).