The colors on the timeline graph of the history-graph-card are kind of random if you use it with “text-sensors” (all colors appear in the same order on every new state and is then used again if that state reappears). If you use multiple graphs to get an overview, you can’t:
(you can see here that e.g. purple is sometimes unlocked and sometimes locked - it’s impossible to see at a glance when which door was locked/unlocked)
Better would be at least fixed colors to states (e.g. calculate a hash of the string).
But better would be customizable colors to highlight good or bad states in the history. This also fits to binary_sensors where often e.g. an open door gets green color and closed door is red (but of course it should be the opposite).