yaros wrote:I think it still looks like water. Is there any other less popular but recognizable way?
Water and ice share a lot of visual properties, sometimes these things are hard to tell apart in photographs too.
The surface of ice is reflective, though tends to be slightly more diffuse (glossy) than still water, so instead of being a direct mirror it tends to be more of a fuzzy reflection. On the other hand, water is not usually still, and in a lot of cases the mirror property of ice is worth emphasizing in contrast... so even a mirror reflection might be appropriate depending on the situation (and/or easier to do with video game technology).
Some kind of reflection goes a long way to establishing the look of the surface, a tree north of the frozen pond casting a weak reflective "shadow" on it might give this impression. Probably fine for this to be some dull darker blue colour rather than reflecting the actual colour of the tree, since palettes are so limited here. This is distinct from a shadow; shadows will fall away from the light source, but reflections fall toward the viewer.
The ubiquitous "diagonal streaks" shorthand is a well established symbol for shiny surfaces. I don't think they're exactly realistic, but part of what makes a surface appear reflective is that as you move, the reflection moves too with your angle of view. In the absence of camera motion, maybe this is a stand-in for the transient patterns of bright light reflecting from it? Reflections from the sun or other bright light do kind of produce patterns, but not really in diagonal streaks.
Also, in the case of ice, there tend to be cracks, scratches and faults that show up as white or light lines, especially on the surface where snow may stick to them. White streaks may serve a dual purpose for that.
The other big property of ice's look is its translucency. It tends to be fairly clear, so you can see what's underneath, especially where it is not too thick. This makes drastic colour changes at the edges where it's shallow, but at the north edge from a perspective like this you might have an opportunity to express "depth" there. (Dougeff's Minish Cap link has a good example at the top right of the article.) An embedded object visible below the surface, like a rock, etc. might give some feeling of depth beneath the ice too.
All of these things are rather difficult to express with 3 or 4 colours like on the NES, though, so good luck!
(Though on the subject of luck... maybe take a look at Lucky Penguin
for inspiration? It uses a novel technique to increase the palette range... but its art looks pretty nice even in a static screenshot that doesn't pick up the technique.)