The temperature calibration for cool stars and in particular the Miras continues to be contentious. Lunar occultations have provided radii for many K and M stars and a good temperature calibration has been derived for the hotter non-variable M stars (Ridgway et al. 1980). The situation for the Miras and carbon stars and the metal-rich and metal-poor M stars is, however, not so clear cut. Observations are generally made in some broad-band color such as (R-I), (V-K) or (J-K) and a temperature derived using either the Ridgway et al. (1980) empirical scale or a black-body scale; differences can amount to several hundred degrees. We decided to theoretically explore the effects that extension, metallicity and pulsation could have on colors.