Even then it’s often ambiguous what is meant. If you have a single handle (on a faucet or shower) which is rotated to adjust temperature, it’s often unclear whether it’s the position of the part of the handle you hold or the other end (which moves in the opposite direction) that indicates the desired temperature
Some faucets have little red/blue symbols to show hot/cold water, but it’s not universal. I wish it was.
Even then it’s often ambiguous what is meant. If you have a single handle (on a faucet or shower) which is rotated to adjust temperature, it’s often unclear whether it’s the position of the part of the handle you hold or the other end (which moves in the opposite direction) that indicates the desired temperature