Dear Peter Wirtz ,

for example please have a look at Fig. 6.4 ( page 45) of:

Working Paper BASICS IN SOLAR RADIATION AT EARTH SURFACE

and Fig. 6.5 at page 47 at:

Technical Report BASICS IN SOLAR RADIATION AT EARTH SURFACE -REVISED VERSION #3

It shows solar irradiation spectra at ground level for different incident angles.

The influence of the atmosphere is shown for the 30° incident case in Fig. 6.4 at page 45 (last link).

The changes (due to latitude) are mainly in overall intensity. But the spectral character (colour) is, to my opinion, nearly the same. There is only a very slight blue shift when going from 0° to 60°.

Roughly estimated flux ratios directly taken from the spectra at 500nm and 800nm:

at 0° ratio I(500nm)/I(800nm)~1,59

at 30° ratio ~ 1,61

at 60° ratio ~ 1,68

So for the tropics ( 0° to ~ 30°) this 'color change' is very small.

So my impression is, that (if there is a latitude dependence on the solar irradiation at all) the color of the starfish is not caused by the color of the sun light, but might be dependent on its maximum intensity. But I must admit, that the intensity change within 0 to 30° is also quite small.

Here is another one, concerning gastropods:

Miura et al. 2007 Temperature-related diversity of shell colour in the intertidal gastropod Batillaria. Journal of Molluscan Studies 73, 235-240.

Article Temperature-related diversity of shell colour in the interti...

Maybe you find something in here... but on different species... :)

https://www.nature.com/articles/s41598-021-98550-3

This phenomenon can be also attributed to a cryptic fitness. Both environment and the trophic level of species may determine the frequency of morphological traits. The climate itself and the irradiance variation favor determined vegetation or soil types, this defines the landscape physiognomy, its "color palette". Traits benefiting predator avoidance prevails, as well as traits favoring sexual selection.Article Gray plumage color is more cryptic than brown in snowy lands...

Good point.