Header with two colors?

My initial thought is using a background image, positioning it to the left and setting it to no-repeat.

However, if you can link me to that site I can see how they did it and let you know :)

Kind of worked just needs to be tweaked for smaller devices. Original site is here though http://anpsthemes.com/industrial/demo-1/

Semmes that there is something to do with the .logo:before pseudo class or something...

Ah, you could try something like that..

.site-logo::before {
    background-color: #000000;
    content: "";
    height: 100%;
    position: absolute;
    right: 100%;
    top: 0;
    width: 1200px;
}

Hi Tom,
Thank you for your reply but it seems that it is not working.

What do i have so far from customizer:
Background: default (white)
No background image for header
Header width: full
Inner Header Width: contained

Any chance you can link me to your site with the above CSS added?

Hi Tom,
Yes, sure. Please see here http://bit.ly/2hTHCul

Alright, let's try this complete CSS:

.site-header {
    overflow-y: hidden;
}

.inside-header {
    position: relative;
    box-sizing: border-box;
}

.site-logo::before {
    background-color: #000000;
    content: "";
    height: 500px;
    position: absolute;
    right: 100%;
    top: 0;
    width: 1200px;
}

Hi Tom,

Thank you. This on almost worked... Left from the logo is changed now but the logo background is not yet. Please see the site again, your code is added.

Here we go:

@media (min-width: 769px) {
    .site-logo::before {
        background-color: #3598DB;
        content: "";
        height: 500px;
        position: absolute;
        right: calc(100% - 247px);
        top: 0;
        width: 1200px;
        z-index: 1;
    }
    .site-logo:after {
        border-left: 0 solid #3598DB;
        border-right: 120px solid transparent;
        border-top: 144px solid #3598DB;
        content: "";
        height: 0;
        position: absolute;
        left: 247px;
        top: 0;
        width: 0;
    }
    img.header-image {
        position: relative;
        z-index: 2;
    }
}

Excellent! Just excellent!

Thank you so much, Tom! Can i buy you a beer over Paypal or something?

You're very welcome - thanks for working through it with me :)

Beer is always appreciated!: https://generatepress.com/ongoing-development

Thanks!