I have pictured Titans lakes and seas as being thick and black.
Oil keeps coming to mind when I think about what it would be to stand on the shores of a Titan lake or sea. But maybe they are not so thick and dark as oil.
If Titan's lakes were pure methane, I suspect they would reflect much of the orange light filtering through the clouds.
On a world with clear skies that has almost pure methane oceans, I picture them as being a deep blue or maybe a purple blue.