Well, I must admit my knowledge is limited espeically when it comes to these things as a solid. In liquid form, at least methane, ethane, propane, butane, acetylene, and ethylene are all clear/colorless. All when pure will be clear, though I do not know about color for ammonia (I think colorless), ammonia hydrate I think colorless), argon, and nitrile oxides - I have little to no experience with them but I would expect them all to be colorless. You mention curiosity in regards to a methane lake - Well seeing as methane is clear and colorless as a liquid, it would come down to other factors such as depth, sediment, and atmosphere. It would be pretty similar to water really.
As solids, they would form some kind of crystal form, though the size and appearance could vary. They could all likely be broken into a power-like form though, which I think would be more common. For color.. from what I have learned, I know conjugated double bonds result in color, which none of these have. I do not know if what other factors may exist which can result in color.
Others may be able to provide more information, but hopefully this is at least a step in the right direction.