How to create new set of color styles in Bootstrap 4 with sass

I'm starting to navigate through the wonderful Bootstrap 4 and I'm wondering how to add a whole new set of elements color to the _custom.scss

Example: Right now you have btn-danger, text-danger etc... how to create for example, using a random name: "crisp" set... so you will have btn-crisp, text-crisp etc...

My guess would be to start with adding a variable

$brand-crisp: #color !default;

But, then what? Thanks! I appreciate your help.

There is not an all inclusive color mixin, so I think you need to use the mixins individually...

.btn-custom {
    @include button-variant(#cece19, #222222, #cece19);
}

.btn-custom-outline {
    @include button-outline-variant(#222222);
}

.card-custom {
    @include card-variant(#aa9999, #997777)
}

http://codeply.com/go/MKGQCrLwDs

Update: In Bootstrap 4, you now can create a new custom "theme-color" to as explained in my answer here. This will allow you to use the color anywhere such as btn-custom, text-custom, bg-custom, etc...

Update Bootstrap 4.1

The button mixins have changed slightly and now require add'l params...

.btn-custom {
    @include button-variant(#cece19, #222222, #cece19, #cece19, #cece19, #cece19);
}

.btn-custom-outline {
    @include button-outline-variant(#222222, #cece19, #222222, #cece19);
}

@import "bootstrap";