It's for a solar garden light with a 1.2V ni-cad battery charged from a tiny solar panel but I can design something (solar or non-solar) for use with 18650's or whatever. The light constantly changes color every few 100 msecs.
These are RGB LEDs
One leg for each color and 4th leg either anode or cathode. Then they require a controller. By mixing the ampacity to each leg they can emit any color. They also come in strips/cords with a premade controller as a unit.
For solar use you will need to determine what voltage and ampacity you can provide and then determine if it will support the lights you are designing for. With these they can slowly change to any color by mixing the RGB intensity to do so or simply jump from one color to another without any slow fading. It all depends on how you program them or the capabilities of the premade controller.
I have many solar garden lights that came with a steady white LED. I bought some colors changing decorations that were powered by a disposable battery. I replaced the white LED on the solar light with the colors changing LED and added a Schottky diode in series with it and added a 0.1uF capacitor as a filter. Now I have many solar garden lights with a colors changing LED.
Some colors changing LEDs slowly change colors and other LEDs quickly and slowly blink the different colors in a pattern.
A colors changing LED has a clear case to show the 3 LED colors, an IC inside to change the colors and only 2 wires.