Correlation does not (necessarily) equal causation.
I think the colors can be explained by: 1. Picking four contrasting colors, 2. Putting them in spectrum order (red to blue), 3. Avoiding dark blue (as the light under the key might not be apparent).
If Elektron were given a do-over, they might lighten up the green, T3 key, as the the lighting under the key is obscured.
I feel like this has been covered before. The colors on Digitone were influenced by the various colors on the front panel of the DX-7, or something like it.