The Schedule a Tour form does have some areas with color that may not fit your branding. (The send button has it's own CSS which you can find here)
Outside of the send button, you'll notice little blue checkmark icons activated when a selection is made and a blue underline
To change the color of the underline:
.sidx-container .sidx-toggle-bar .sidx-toggle-bar-item.sidx-selected, .sidx-container .sidx-toggle-bar .sidx-toggle-bar-item:hover {
border-bottom: 2px solid #hexcode !important;
}
To change the checkmark:
.sidx-container .sidx-toggle-bar .sidx-toggle-bar-item.sidx-selected:before {
color: #hexcode !important;
}
Remember, place this code in the custom CSS box under Settings > Design. Clear your caches and check your web page in an incognito browser to see the change!