That's because the ones that change to gray, are trap tiles, and it's only only if you have high enough perc to see traps. Problem solved, no further testing required. Just saved you 15 teleports into prison farm, You're welcome
Cloun you ruin everything! Also I did not know that lol.
While I'm on topic of prison. The last 3 times I went to prison Edge there have been no arch templars by the chest