I took a photo of light beam that penetrating water surface (top right circle is the water surface, bottom left circle is the bottom of water container).
Is there any physical explanation on why top-right is blue and bottom-left is red?

My hypothesis is : light moves slower inside water medium, that's why the photon's energy is weaker now, thus redshifted from blue (high energy) to red (low energy).

But somehow, i still have a doubt in my own hypothesis. Is there any other explanation?