When you download the theme with a copy of jQuery UI it appears in the file
jquery-ui-1.8.nn.custom.css. Within that file should be a link containing all the theme settings to allow you to go back and change it. In the sample I downloaded it appears at line 50 and looks like this:
- * To view and modify this theme, visit http://jqueryui.com/themeroller/?ffDefault=Trebuchet MS, Tahoma, Verdana, Arial, sans-serif&fwDefault=bold&fsDefault=1.1em&cornerRadius=4px&bgColorHeader=f6a828&bgTextureHeader=12_gloss_wave.png&bgImgOpacityHeader=35&borderColorHeader=e78f08&fcHeader=ffffff&iconColorHeader=ffffff&bgColorContent=eeeeee&bgTextureContent=03_highlight_soft.png&bgImgOpacityContent=100&borderColorContent=dddddd&fcContent=333333&iconColorContent=222222&bgColorDefault=f6f6f6&bgTextureDefault=02_glass.png&bgImgOpacityDefault=100&borderColorDefault=cccccc&fcDefault=1c94c4&iconColorDefault=ef8c08&bgColorHover=fdf5ce&bgTextureHover=02_glass.png&bgImgOpacityHover=100&borderColorHover=fbcb09&fcHover=c77405&iconColorHover=ef8c08&bgColorActive=ffffff&bgTextureActive=02_glass.png&bgImgOpacityActive=65&borderColorActive=fbd850&fcActive=eb8f00&iconColorActive=ef8c08&bgColorHighlight=ffe45c&bgTextureHighlight=03_highlight_soft.png&bgImgOpacityHighlight=75&borderColorHighlight=fed22f&fcHighlight=363636&iconColorHighlight=228ef1&bgColorError=b81900&bgTextureError=08_diagonals_thick.png&bgImgOpacityError=18&borderColorError=cd0a0a&fcError=ffffff&iconColorError=ffd27a&bgColorOverlay=666666&bgTextureOverlay=08_diagonals_thick.png&bgImgOpacityOverlay=20&opacityOverlay=50&bgColorShadow=000000&bgTextureShadow=01_flat.png&bgImgOpacityShadow=10&opacityShadow=20&thicknessShadow=5px&offsetTopShadow=-5px&offsetLeftShadow=-5px&cornerRadiusShadow=5px
