I believe you mean the fishes mucoprotective slime coat. It is there to protect the fish from things (bugs/chemicals/etc etc) in the water that may damage it.
"Mucis" is not a word. Did you mean "music" or "mucous"?
I would expect them to have no effect on Goldfish whatsoever.
no
Whit and thin liquid
no
yes
mucis
yes, it will
Different types of goldfish food typically don't affect the colour of goldfish, however there are some specific goldfish foods that may enhance the color of goldfish- but do not change its overall color.
Well pH has an affect on goldfish health: too low or too high a pH causes the fish to be stressed and if it is stressed it is more susceptable to disease and will not grow.
Let mucis begin and hear you Heart beating
It depends on the conditions. If all the goldfish were being starved (for example) most of them WOULD die. But if one just happened to die for no particular reason, then it probably won't affect the rest.