Some help, not an answer.
To do this you will need to modify the sidebar tabs tiddler, I would suggest using the colour field on the tiddlers that make the sidebar tab and using that.
One issue is you may need modify the tabs macro as well, or perhaps clone and rename the copy the existing one.
I will investigate further if no better answers are posted.
Regards
Tony
/* SIDEBAR TABS */
.tc-sidebar-lists .tc-tab-buttons button {
color: #0044BB;
background-color: #FFFFFF;
border: 1px solid #D1DDF3;
border-radius: 0.3em;
}
.tc-sidebar-lists .tc-tab-buttons button.tc-tab-selected {
font-weight: bold;
color: #0044BB;
background-color: #D1DDF3;
border: 1px solid #A2BBE6;
border-radius: 0.3em;
}
/* SIDEBAR 'More' TABS */
.tc-more-sidebar > .tc-tab-set > .tc-tab-buttons > button {
background-image: none;
background-color: #FFFFFF;
border: 1px solid #D1DDF3;
}
.tc-more-sidebar > .tc-tab-set > .tc-tab-buttons > button.tc-tab-selected {
background-image: none;
background-color: #D1DDF3;
border: 1px solid #A2BBE6;
}
Maybe this can help.