A fine-tuning of the emission chromaticity from red to green is, reported for organic-inorganic nanostructured hybrids co-doped with Eu3+, Tb3+, and Tm3+. Raising the temperature from 200 to 300 K changes the color coordinates smoothly from the 1 yellowish-green region of the chromaticity diagram towards the red. This is discussed in terms of thermally activated energy-transfer mechanisms from Tb3+ energy states to the hybrid's emitting levels.