Modern tomato breeding practices have selected for fruit with a uniform light-green color before ripening, a trait that promotes even ripening at the cost of reducing fruit sugar content. This trait, which is determined by the quantity and distribution of chlorophyll in the unripe fruit, is controlled by a single recessive locus uniform ripening (u). Ann Powell and colleagues (Science 336, 1711–1715, 2012) now show that the u/u trait is caused by a loss-of-function mutation in SlGLK2, which encodes a transcription factor known to regulate chloroplast formation. The authors mapped the u locus to a 60-kb region on chromosome 12. They then sequenced SlGLK2, the top candidate gene in the region, and identified a 1-bp insertion shared by all u/u varieties that results in a frameshift and premature termination of translation. Co-suppression of SlGLK2 in U/U plants produced unripe fruit that was uniformly light green. Conversely, expression of Arabidopsis thaliana GLK2 in u/u tomato fruit before ripening produced unripe fruit that was uniformly dark green and whose sugar content was increased by 40% after ripening. Application of these findings could lead to improvements in tomato fruit quality and production traits.