An array of fully isolated multi-junction complimentary metal-oxide-semiconductor (CMOS) filterless color imager cells is provided, with a corresponding fabrication process. The color imager cell array is formed from a bulk silicon (Si) substrate without an overlying epitaxial Si layer. A plurality of color imager cells are formed in the bulk Si substrate, where each color imager cell includes a photodiode set and a U-shaped well liner. The photodiode set includes first, second, and third photodiode formed as a stacked multi-junction structure, while the U-shaped well liner fully isolates the photodiode set from adjacent photodiode sets in the array. The U-shaped well liner includes a physically interfacing doped well liner bottom and first wall. The well liner bottom is interposed between the substrate and the photodiode set, and the first wall physically interfaces each doped layer of each photodiode in the photodiode set.