Besides, is the OW the most important thing in a hack?
The cement blocks in the ghost house are a nice change of pace, something not found often in GHs.
The Ow is one of the most important things. If you dont have one you can't play. I would say the levels are the most important thing.
You have a point that the cement blocks are not often used in ghost houses, but it is not good to use them in large amounts.
Are the path ways somhow messed up? I had this problem. I fixed the pathway then it worked. I might not be that thought when exit the level are the settings right? In edit level tile settings you can set which way mario will go that also might be the problem.
Ohh I didn't see the "how". (and I don't know how i missed that.)
Press the rainbow star that is to edit palette. Look through different world pallets to see what changes. (water color, land)
Then experiment by changing some of the color. I would make a copy of your rom incase you accedentally mess somthing up (like i did, but i had a copy)