It seems that the "Choose Direction" dialog (Ctrl-Click on the icon of an extension building with rotations) always displays player color as the first players color.
Bild_2024-11-27_200857210.png
As you can see in the screenshot, the current player is "Napik" and blue, but the extension is shown in "Simutrans-Spieler"s red.
(And just to make sure: Yes, it's supposed to be player color and displays correctly when placed)
Should be fixed in r11442.