I found that if you give the water options event (which happens to change nothing else than the color of the water) two parameters of 8 bits, changing the first parameter will only change the water surface and changing the second will only change the rest of the water. Also, setting both parameters to the same value will cause the water to be completely in the same color. Because there are 256 values possible for each parameter, I'd say the value refers directly to a palette entry.

-If there is anyone who could think of another way this parameter is used, please say so.
-If you know a way of getting the palette for the Binnen-tileset, then say so as knowing the palette would really help me to check if the water options parameters really refer to palette entries.

EDIT: thanks to n0 for reminding me about F12 I got the palette =) Now checking the parameter values
EDIT2: checked and I were right.