JKC wrote:
It appears that some Myrtle Crapes are brighter or more colorful than
others, even if they are of the same color. Some red MC's appear to
be deeper red than others. Some pink ones seem to be brighter pink
than others. Am I seeing things clearly, and there are indeed
different shades of colors? Can I control the shade of the color
with watering, fertilizer, etc.?
If so, how do I produce deeper/brighter colors?

Crape myrtles come in different named varieties. To get a different color,
you'll have to plant a different variety.