Yellow (Munsell) (#EFCC00)

/* Background */
.element {
    background-color: #EFCC00;
}

/* Text */
.element {
    color: #EFCC00;
}

/* Border */
.element {
    border: 1px solid #EFCC00;
}

/* Linear gradient to complementary */
.element {
    background: linear-gradient(
        to right,
        #EFCC00,
        #DFE4FF
    );
}

/* Radial gradient */
.element {
    background: radial-gradient(
        circle,
        #EFCC00,
        #DFE4FF
    );
}

// SCSS variable
$yellow-(munsell): #EFCC00;

// With RGB channels (useful for rgba() usage)
$yellow-(munsell)-r: 239;
$yellow-(munsell)-g: 204;
$yellow-(munsell)-b: 0;

// Usage
.element {
    background-color: $yellow-(munsell);
    color: rgba($yellow-(munsell)-r, $yellow-(munsell)-g, $yellow-(munsell)-b, 0.8);
}