Hi.
It might be better to use 'On Trigger Stay' instead of 'On Trigger Enter'
and you can find some actions on the
Ecosystem to set the color instead of using set property
Now i do think you setup is wrong, try this :
After 'Create GameObject' use the 2 trigger events only once to know on spawn if it can place or can't. and remove the Get Fire1 Down action
Then in reset color add a trigger2D Event (On Trigger Exit) and conntect to 'Can't Place'
Also add the 'Get Fire1 Down' and connect to 'has building'.
Then in 'Can't Place add a trigger2D Event (On Trigger Stay) and connect to 'reset color'
I hope you understand, if not let me know and i will make a sample tomorrow.