1. Change text color to black using CSS.

2. Change background color from any colors to grey using CSS.

3. Turn all images to black & white using CSS.

img
{
  -webkit-filter: grayscale(1); /* Older Webkit */
  -webkit-filter: grayscale(100%);
  -moz-filter: grayscale(100%);
  -ms-filter: grayscale(100%);
  -o-filter: grayscale(100%);
  filter: grayscale(100%);
  filter: url("data:image/svg+xml;utf8,<svg xmlns=’http://www.w3.org/2000/svg’><filter id=’grayscale’><feColorMatrix type=’matrix’ values=’0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0 0 0 1 0’/></filter></svg>#grayscale"); /* Firefox 4+ */
  filter: gray; /* IE 6-9 */   
}

You can specify !important to overrides the style.

color:black!important;