Expanding on ‘more photosynthetic organelles which specialize in different wavelengths’, one obvious choice is microbial rhodopsin - which seem in simplified terms to be very basic pumps to generate ATP from the wavelength of light they best absorb (green-blue light, thus appearing purple). Simpler than photosynthesis (doesn’t fix carbon) and the source of our own monochromatic low-light vision. They also tend to coexist with photosynthetic species as they don’t directly compete for wavelengths of light and may benefit from compounds those produce.
The simplified form seems pretty similar in implementation to rusticyanin’s current implementation, using a different resource.