The invention relates to a color-tunable illumination system (10; 12; 14) and a luminaire. The color-tunable illumination system comprises a first light source comprising a first set of light emitting diodes (21, 24), and a second light source comprising a second set of light emitting diodes (31, 37, 34). Both the first and second light source emit light of substantially a first predefined color into a light mixing chamber (60). The light mixing chamber further comprises a first luminescent material (50) converting light of the first predefined color into light of a second predefined color. The first light source is positioned with respect to the first luminescent material for illuminating the first luminescent material with a first flux of light being part of the light emitted by the first light source into the light mixing chamber. The second light source is positioned with respect to the first luminescent material for illuminating the first luminescent material with a second flux of light being part of the light emitted by the second light source into the light mixing chamber. The first flux is different from the second flux. The effect of the measures according to the invention is that a change in the intensity of the light emitted by the first light source relative to the intensity of the light emitted by the second light source results in a change of the color emitted by the color-tunable illumination system.