Tip: Bad things to do in the title demo: Enter a door or a pipe, activate a P-switch or a star, complete the level, hit a message block, or die. These will either glitch the music, or force the player into an endlessly looping title level until they reset the game.
I have a level where I want to edit the palette, so naturally I just checked "Enable Custom Palette" and clicked on the star icon. Everything worked fine, but there's one small snag. One color simply refuses to stay changed. It's Palette 6, Color 4, and I changed it to a grey color. It works fine, but as soon as I switch to a new level and come back, the color is back to yellow. When I test it, I notice that this particular color flashes. I don't know much about SMW hacking, so is this a special color?