Three-way switch wiring behaving oddly
As many answers and many more diagrams discuss here, color-coding is absolutely meaningless in 3-way circuits.  The only exceptions are if


someone deliberately marks the wires with colored tape (I use yellow for both travelers, no need to distinguish them from each other) or
the work is in conduit and someone used two oddball colors (I use yellow-yellow) for the travelers.


throws up hands Aww, why not? 3-ways are a morass of senseless color coding and absolute lack of marking.

because that's the way 3-ways work.  Seriously.



And this seems to be a confusion: expecting &quot;up/down&quot; to correspond to &quot;on/off&quot;. They won't.  Go get a 2-way switch and hold it in your hand. See where it says &quot;On&quot; and &quot;Off&quot; on the lever?  Now look at a 3-way switch. No markings.
Note that in the above diagram, the left switch is &quot;up for off, down for on&quot;.
In the 3-way world, there are only 2 states: the state the light is in; and the other state.  Throwing the switch once changes the state.  That's it.
So if you want &quot;Up&quot; at this 3-way location to be &quot;on&quot;, you can swap wires all day (it's actually easier to just flip the switch over).  However this effort will be wasted the moment someone throws the other switch in the 3-way circuit; now this switch will be &quot;upside down&quot; again.
Suppose you flipped the left switch above; then somebody throws the right switch.  Now you have to start over.
That's how 3-ways work.
If you just can't stand it, try looking for a 3-way switch which is a pushbutton instead of a toggle.  Making them toggles like they did really pains my OCD.