Salmon eggs (roe) range in color from pale yellowish-orange to dark reddish-orange. The color varies both by species and within species and is determined by water temperature, sediment composition, age, and other factors.
Scientists believe that salmon navigate by using the earth’s magnetic field like a compass. When they find the river they came from, they start using smell to find their way back to their home stream.
Some salmon will try to find the right stream until they use up all their energy and die, but most would simply try to find other salmon with which to spawn. 
Many man-made objects hurt salmon by blocking their migration route or making migration much more difficult. Dams on rivers are the main obstacle to salmon migration. Other man-made objects are designed to help salmon, like fish ladders.
Engineers design fish ladders to make it easy for fish to ascend. Each step of the ladder is a gradual increase in height and there are places for fish to rest.
Salmon eggs are very sensitive to movement early in their development so they are not moved until they are 'eyed' (their eyes are showing through the egg). They are handled gently and either kept in water or kept moist and cool during transport.
Salmon change color to attract a spawning mate. Pacific salmon use all their energy for returning to their home stream, for making eggs, and digging the nest.
We don't know. They must have a genetic cue to head downstream when their bodies are ready to change to a saltwater environment (they are called salmon smolts when their bodies change and they migrate to the ocean).
Salmon eat insects when they are young and eventually eat other fish when they are older.Learn more:Salmon (NOAA FishWatch)
Each female salmon can have between 1,500 and 10,000 eggs. Only a few (0 to 10) of these eggs will survive to be adult salmon.