Habluka's Weekly Challenge #1

[tempest]

but it seems to be unreadable and I don't know why. It looks to be a forum problem and I kindly ask a moderator to investigate it.

Not a forum problem. You were using GIFs, which have only binary opaque/transparent values rather than a separate alpha channel. Therefore smoothing is done in color, and in this case, it was for a white background. Fixed by using PNG instead (still less than optimal readability because it's black, though).