Hello Charlotte ! 
1. If you want ANY color applied to featured image in the page, you can add the following code to the Header Code: 

 <style>
.page .banner.cover:before {
    opacity: 0;
}
</style>

 
2. To change the color for the main menu, you can add the following code to the Header code:

 <style>
.nav-main a {
     color: #...;
}
.nav-main li a:hover, .nav-main li a:active, .nav-main .active > a, .nav-main li:hover .sub-nav-open, .nav-main .active .sub-nav-open {
     color: #...;
}
.nav-main .navbar-nav > .active {
    border-bottom-color:  #FFF;
}
</style>

 
3. To change default color for the title, you can add the following code to the header :

 <style>
.post .entry-inner .entry-title > a {
    color: #....;
}
.post .entry-inner .entry-title > a:hover {
    color: #....;
}
</style> 

 
4. To change the Heading font and button text, you can add the following code to the Header Code:
—Heading font—–

 <style>
.home .banner .page-title {
    font-size: 80px;
}
</style>

— button text—–

 <style>
.banner #get-started {
     font-size: 11px;
}
</style>

 
5. If you want to display the Page header, you can add the following code to the Header Code:

 <style>
.page-header {
    display: none;
}
</style>

Hope this helps !