photometry will anyhow probably hamper any temperature determination below $10000$ K (a 0.05 mag photometric error can bring any $10000$ K star on the $9000$ K star locus). Above that value, the precision on the temperature determination depends on the temperature itself, but is typically of a few thousand Kelvins for colour indices accurate to 0.05 mag and for stars in the middle of the temperature domain. Such accuracy allows a reddening determination with a precision of about $\sim~0.3$ magnitudes in $A_{\rm V}$ at any but the “coolest” temperatures ($<~11000$ K).

The situation is slightly worse when one includes giant stars as well since the temperature tracks for the giants at a given reddening cross those of the less reddened MS stars. Even worse, they pass below the locus of the $9000$ K MS stars at $\sim~10500$ K. As any place below this line can be occupied by stars with various combinations of temperature and reddening, the domain in which a temperature determination is possible for giants is restricted to stars above $\sim11000$ K. As one does not know [*a priori*]{} whether or not a star is a giant, this of course also sheds some uncertainty on the temperature and 