how to change the color of the placeholder text?

This is controlled via css. The code i used on a recent project is below ignore the @font-primary this is a less variable. You can switch out with any valid font for the font-family property.

::-webkit-input-placeholder {
  font-family: @font-primary;
  color: #999999;
  font-size: 14px;
}

:-moz-placeholder { /* Firefox 18- */
  font-family: @font-primary;
  color: #999999;
  font-size: 14px;
}

::-moz-placeholder {  /* Firefox 19+ */
  font-family: @font-primary;
  color: #999999;
  font-size: 14px;
}

:-ms-input-placeholder {
  font-family: @font-primary;
  color: #999999;
  font-size: 14px;
}