.rainbow2 {
background-image: -webkit-linear-gradient(left, #E0F8F7, #585858, #fff); /* For Chrome and Safari */
background-image: -moz-linear-gradient(left, #E0F8F7, #585858, #fff); /* For old Fx (3.6 to 15) */
background-image: -ms-linear-gradient(left, #E0F8F7, #585858, #fff); /* For pre-releases of IE 10*/
background-image: -o-linear-gradient(left, #E0F8F7, #585858, #fff); /* For old Opera (11.1 to 12.0) */
background-image: linear-gradient(to right, #E0F8F7, #585858, #fff); /* Standard syntax; must be last */
color:transparent;
-webkit-background-clip: text;
background-clip: text;
}
.rainbow {
background-image: -webkit-gradient( linear, left top, right top, color-stop(0, #f22), color-stop(0.15, #f2f), color-stop(0.3, #22f), color-stop(0.45, #2ff), color-stop(0.6, #2f2),color-stop(0.75, #2f2), color-stop(0.9, #ff2), color-stop(1, #f22) );
background-image: gradient( linear, left top, right top, color-stop(0, #f22), color-stop(0.15, #f2f), color-stop(0.3, #22f), color-stop(0.45, #2ff), color-stop(0.6, #2f2),color-stop(0.75, #2f2), color-stop(0.9, #ff2), color-stop(1, #f22) );
color:transparent;
-webkit-background-clip: text;
background-clip: text;
}
<span class="rainbow">Rainbow text</span>
<br />
<span class="rainbow2">No rainbow text</span>