Well the shades of blue in the screenshots on the website look fine to me.
The first question is, of course, what is a "normal" map for Joop, which depends
on purpose (car navigation, waterway navigation, hiking) as well as on cultural
background.
In Europe, motorways are often rendered blue, thus the water needs
to differ from that.
For car navigation, water is just a landscape feature such as meadows,
forests or residential areas, so it is good to have that in more pale tones.
I have sampled the R/G/B values in the screenshot on the website:
66/28/255 for the proposed route ahead (dark blue)
132/154/255 for the motorway
181/211/214 for the water features, which has a bit more R/G in it
to make it lighter, but well suited for the purpose of car navigation.
How distinguishable that is for a particular user might also depend on
his screen adjustment and calibration.
t.