using gradient but without mixing color

When you did:

background: linear-gradient(to right, #000 28%, #fff 72%);

it means: Black (#000) from 0% to 28%, then start a gradient to white (#fff) until reach 72% and after this gradient, use white until the end.

So you can use:

background: linear-gradient(to right, #000 28%, #fff 28%);

This way you'll get: black from 0 to 28%, a gradient from 28% to 28% (it means, no gradient), and white from 28% to the end. So you'll get only back and white, without the gradient between them.

try this

.div{
    background: -webkit-linear-gradient(left, black 50%, white 0%);
    background: -moz-linear-gradient(left, black 50%, white 0%);
    background: -ms-linear-gradient(left, black 50%, white 0%);
    background: linear-gradient(left, black 50%, white 0%);
}