What does it mean if there are two different alleles for a trait?

In a trait of let's say hair color, two alleles can be brown or black hair.
In a trait of skin color, two alleles can be dark or light.
In a flower's trait of petal color, two alleles can be purple or white.

Using these alleles, you can determine offspring traits

The moths will eventually become extinct

Photo means light and synthesis means combination so combination of light