Yes, if you are changing the colors now in the style properties, they won't change in the frontend. You need to adjust the color code in the extra.less template now.
Simple browser inspector tool.
Add this to your extra.less:
[data-notice-id="-1"].notice--cookie .js-noticeDismiss.button--notice.button, .notice--cookieAdvanced .cookies-buttons .button--primary {
color: #fcfcfc !important;
background: #e8264d !important;
}
See if it changes anything.
Settings in style properties should work for these buttons too. It works fine on my side. Maybe it is overwriting something (from extra.less?).
You can do it manually with this in your extra.less template:
@media (min-width: @xf-responsiveMedium) {
.u-bottomFixer [data-notice-id="-1"] {...