I think he's saying he doesn't like the way the swirl design looks.
Maybe redraw it or make another design.
And Knytt Stories would lag if you use too many of those glowing tile objects.
What I was thinking was that you would use the dark tiles (as in minmay's suggestion) in your tileset and put one or two of the glowing tile objects in some rooms.
Another suggestion: You should see the cave at the end of Dark Sky of Wish Mountain (by AlmightyZenTaco) (coordinates 1019, 998, if that helps) and how it uses default tileset 63. Maybe you could get some inspiration from that.