Leaf chlorophyll (Chl) is emphasized as an indicator for photosynthesis in wheat (Triticum aestivum L.). SPAD greenness meters are used to predict extractable Chl, but few studies have evaluated relationships between flag leaf greenness and Chl among wheat genotypes. Sixteen spring wheat genotypes with similar development patterns were studied in eight environments (2 years, 2 irrigation treatments and 2 sowing times) to investigate the precision of the SPAD-502 meter to predict Chl content/concentration. Relationships of Chl with SPAD greenness generally best fit linear and quadratic models. Relationships of SPAD greenness with Chl concentration were weak and inconsistent. Strongest associations were observed with Chla content (highest R2 = 0.71 under late sowing), whereas associations with Chlb content were weak (highest R2 = 0.46) or insignificant. Relationships between SPAD greenness and total Chl content ranged from low (R2 = 0.24, p = 0.054) to moderate (R2 = 0.64, p < 0.001) under rainfed conventional-sowing and late-sowing conditions in the second year, respectively. SPAD greenness can be used to diagnose spring wheat genotypes differing in flag leaf Chla and total Chl content under warm Mediterranean conditions, but may not always applicable in cooler Mediterranean conditions, where genetic variability, especially in Chlb, was not expressed adequately.