By changing the base_color and flow_color in fuilds.lua to this:
pneumaticFluid.base_color = {0, 0, 0}
pneumaticFluid.flow_color = {1, 1, 1}
the flow becomes visible, which makes it look much better. Perhaps in the future the fluid color could be decided by the item itself, similar to how this mod does it: https://mods.factorio.com/mod/Automatic_Train_Painter

Snother suggestion I have is to remove the water icon that is put over the item texture, since its already pretty clear that its a fluid when its in a pipe

Not sure how to set the colors based on the item itself (wouldnt that require you to 'read' the icon & create an average color based off of it?), but I will include the suggested change in the next update.