Most liners for ponds are black or grey this is mostly for uv protection to make the liner last longer in the sunlight.
Pre formed ponds are often black for the same reason,But they can be painted in any color you want.
A black pond will give protection against some predatory birds as they will have problems judging how deep the pond is(herons and other wading birds)
A black or dark color will to some degree hide agae growth and make the pond look cleaner.
Fish breeders will often use a light blue or light green pond to show the colors of the fish better.
There is no problem to use any color you want in your pond but the lighter colors get dirty quicker.
If you are making your own fiberglass pond you can buy colored aquarium sand in a pet shop and sprinkle this on the innside of your pond by using a thin layer of polyester as glue(it makes it easier for animals to get out of the water and it looks more natural).