we could be talking about a few different things here.
ACCIDENTALLY CLOSED WINDOWS
1) the color wheel has disappeared. under the windows drop down menu select STYLE EDITOR. this will open the style editor window.
2) the window where your styles (colors) are kept has disappeared. under the windows dropdown menu, select PALETTE. this will open the palette window.
OR PERHAPS BOTH OF THOSE WINDOWS ARE STILL OPEN BUT THE STYLES ARE MISSING FROM YOUR PALETTE WINDOW (STYLE BOX IS EMPTY) AND YOU SEE THE WORDS "-NO STYLES-".
palettes are connected to levels so when you create or select a level in the xsheet the palette/styles associated with that level will be displayed in the Palette Window.