Chromatic abberation no.1

The rainbow reflections that you see off of glinting water when using a kaleidoscope filter on your camera is most likely caused by a phenomenon called chromatic aberration.

Chromatic aberration occurs when different wavelengths of light are refracted differently by a lens or filter, causing the colours to separate and create a rainbow effect. When you use a kaleidoscope filter on your camera, it can cause the light to refract in a way that creates this separation of colours, leading to the rainbow reflections that you see.

Additionally, the reflections off of glinting water are already somewhat rainbow-like in appearance, as the surface of the water acts as a prism, separating the colours of light that make up white light.

So when you combine the natural rainbow effect of the water with the chromatic aberration caused by the kaleidoscope filter, you get even more vibrant and colourful rainbow reflections in your photos.