Blue Gray (#6699CC)

/* Background */
.element {
    background-color: #6699CC;
}

/* Text */
.element {
    color: #6699CC;
}

/* Border */
.element {
    border: 1px solid #6699CC;
}

/* Linear gradient to complementary */
.element {
    background: linear-gradient(
        to right,
        #6699CC,
        #E6CCB3
    );
}

/* Radial gradient */
.element {
    background: radial-gradient(
        circle,
        #6699CC,
        #E6CCB3
    );
}

// SCSS variable
$blue-gray: #6699CC;

// With RGB channels (useful for rgba() usage)
$blue-gray-r: 102;
$blue-gray-g: 153;
$blue-gray-b: 204;

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