Sure Vic, let me see your URL, please.
What is the mobile header color you want to have?

Thank you so much!!

@media only screen and (max-width: 768px) {
#header {
    background: #254868;
}
}

@media only screen and (max-width: 1017px) and (min-width: 769px) {
#header {
    background: #254868;
}
}

Add this too if you want the mobile menu (the 3 lines) to become white:

.m_nav_ham {
    background: #fff;
}

No problem, just add the !important clause to them then:

@media only screen and (max-width: 768px) {
#header {
    background: #254868!important;
}
}

@media only screen and (max-width: 1017px) and (min-width: 769px) {
#header {
    background: #254868!important;
}
}