The hypothetical "yellow genes" are actually the lack of a gene that codes for an enzyme that degrades carotene. A 40-carbon carotene is snipped into two pieces - a 13-carbon and a 27-C. The latter is then snipped again into a 13-C and a 14-C. These smaller carotenoids can then be oxidized, producing the most potent perfumes: including β-damascone, β-damascenone, β-ionone. These are known as the rose ketones.

The Musk rose and its allies start with different carotenes than the original Tea rose types. Some of the Tea-Noisettes inherit the Musk rose carotenes along with the Tea rose's lack of carotene degrading enzyme(s). Thus, the more deeply colored Tea-Noisettes are showing carotenes that would be degraded and oxidized into perfume in the Musk rose itself. This can be apparent even in crosses between Noisette and Tea, such as Smith's Yellow, where part of the carotenes are degraded but the remainder provide color.

This also occurs in some of the Luciae hybrids, such as François Foucaud. Here, again, the the richness of color is partly due to the Luciae carotenes remaining intact and visible, while the remainder provide a delicious scent.

Similarly, the yellow Banksiaes are less fragrant than the white forms that smell of violets (β-ionone).

Many of the Pernetianas are richly perfumed, often with a somewhat different scent than HPs and other roses. Rosa foetida produces its own distinctive carotenes, which can be degraded and oxidized into equally distinctive scents.